In case you need this too...

My mom (65) was diagnosed over a year ago due to her TBI from 10 years before, but my aunt (87) was diagnosed this week. Her daughter was asking me where to start, so here's the list I gave to her. Some of this is CA specific, but you can use keywords to look in your specific state.

TO-DO LIST
Power of attorney: most places will take walk-ins, but some require appointments. The person signing over the power must be present and 2 witnesses. (We did not do this with mom because she may start off with a good day, and then quickly change. If the person who is supposed to sign over says they do not want to, it will not be signed off on.) https://www.yourlegacylegalcare.com/blog/is-a-power-of-attorney-good-from-state-to-state/
If they are receiving SSI, they need to call and have you added as representative payee. This can be done over the phone, and then they send a form to be signed and sent back.
they need to sign an ROI (release of information) with their current doctors giving you permission to sign and speak for them and once they get a new doctor with you to request the transfer of medical records. ROIs are only good for one year. You can provide their medical provider with a copy of the POA, but if you want any other family member to help out, complete the form for them too.
You are going to want to set them up with a geriatric doctor who specializes in dementia (if over the age of 70). Make an appointment as soon as possible and have them do a new physical and review of their medical history.
While at the doctors, you are going to want to have them complete a 602A form for placement in residential care. Even if you plan on keeping them in your home for a while or as long as you can, get this done ASAP as it can be hard to get in later when you need it last minute. It is good in any state and lasts for one year based on the sign date. Have the doctor write out the name of each medication, their doses and schedule, and what it is for.
You may or may not want to complete an advanced health directive. That is something you can just download, fill out with them, and get a notary to sign with both of you present.
If you do not already have a disability placard, apply for one on the person's behalf. Trust me, on the bad days, it is going to make everything easier.
Order a medical alert bracelet or necklace. Include your phone number and anyone who may be able to help if they ever wanders off. https://www.americanmedical-id.com/
Get respite. We used Care.com and they have some really wonderful people on there. Doing it sooner rather than later will be better in the long run because they have time to become part of the person's routine before it starts to get worse. You can have them do whatever you or the person in your care needs doing: helping them bathe, house cleaning, cooking for them, or just keeping her company.
Depending on how bad they are getting, you may want to apply for IHSS which will pay you or a selected person to help take care of her.
Look into your local county's support for aging. They should have resources available to you that you may not be aware of and may even be able to help you complete the paperwork.
Look into PACE. They act as a daycare for the elderly and will even do all of the appointments for health, dentist, physical therapy, etc. and have meals for them. https://www.dshs.wa.gov/altsa/program-all-inclusive-care-elderly-pace
Things to note:
most memory care homes do not accept Medicare
Save a copy of the POA to your devices so you can send it to any agency that says they need it before speaking with you
Some places are outdated and will ask you to fax them the paperwork
Document EVERYTHING spending wise: what you sold of hers and for how much, and where each sent goes to for her care.

LOCKS AND THINGS
Door knob covers
if you have round: https://a.co/d/dpowBci
if you have levers: https://a.co/d/1XdGDJU
Remove the locking knobs from any doors where they might lock themselves in by accident. If that room still needs to lock for other people (i.e., bathroom), use this type of lock up high out of sight: https://a.co/d/4EQbvGV
Use this on your front door. again, up high and out of sight: https://a.co/d/1sRh0uk
If you have a sliding back door, one of these locks: https://a.co/d/4uDNXU3 or https://a.co/d/1zIbOoK
If you have a French door fridge: https://a.co/d/5vf3TC7
For top freezer fridge: https://a.co/d/1Lk8vnC
For my mom, she was constantly unplugging things including her medical devices, so we had to put these on her plugs in her room: https://a.co/d/8u09P3b
Because my mom kept moving the furniture around and accidentally barricading herself in her room, taking out all her clothes and insisting that had to be washed over and over, we bought her a captains bed and used these to hold the drawers closed and placing them under the mattress so she could not open them on her own: https://a.co/d/fxg8hrN
If there are rooms in the house that do not have doors, but you find you need to keep them out of them for one reason or another, there is this baby gate. I have seen several in my line of work, and this is by far one of the best. https://a.co/d/3JYilia
Things will disappear and end up in weird places. There is no avoiding it. We bolted down what we could, including the soap: https://a.co/d/5Swxb86
For all other drawers and cabinets: https://a.co/d/9H0wFAP
Because we had respite in the house, we used these to help keep an eye on everything: https://a.co/d/gq9TyaC
Get some sort of bell for when the front door or any door leading outside is open (we have an alarm system that says which door was opened): https://a.co/d/06N36bO
Stove knob covers (we did not end up getting): https://a.co/d/aHadpHa
For the shower: https://www.target.com/p/jokari-child-safety-guard-protector-for-sink-shower-knobs-door-handles-childproof-lock-prevents-hot-water-burns-easy-install-1-universal/-/A-92743205?preselect=92743205
Get a handheld shower head

EMOTIONAL THINGS
Take a break when you can. If someone volunteers to sit with them, take it.
Don't fight over the little things (this one was really hard for me). If they say the sky is green and the grass is purple, then that's what it is.
As the day gets later, the worse they may get (sun downing). Mom could start off great first thing in the morning and recall all the things, but by the end of the day before bed, she wouldn't know her own name or who I was.
Keep communication with their doctor. I am lucky that hers has an app we use and I can just reach out to her different specialists and give them updates and they can make changes to her medications as needed. If her sleep patterns change, she is eating more or not eating at all, depression, anxiety, hallucinations, anything, let them know. We were lucky that most of mom's hallucinations were happy or relatively mild.
Keep it simple. don't over explain things as that just frustrates everyone.
Keep them engaged and busy. There are lots of cognitive things that can be done naturally such as folding and putting away clothes, reading, doing daily words or reciting what they have done so far. We had this journal in the beginning with mom, but then she lost the ability to write or read. It worked pretty well while we were able to use it because I would sit with her and help her complete it for the day. https://a.co/d/5n85M1e
Seek out help whether it has to do with them or just someone to do the little things that you can't anymore because of you being busy with them.
Your emotions are totally valid no matter what they are. Everyday I went through them all: sad about what she was going through; angry that there was nothing we could do; tired of having to take care of her; dreading what might come next; guilty about the last two. Let your doctor know what you are going through because they might have resources for you as a caregiver as well.