Sister Financially Abusing Mom

My 54 year old sister is a narcissist and is the primary caregiver for our mom. Although I use caregiver very loosely. My mom has lived with my sister for 6 years now. The first 4 years while she was married. My sister gets paid by in home support services to “take care” of my mom. Help with meals, bathing, doctors appts, medications, etc. However, she does not cook so mom has to make herself sandwiches or eat salads because my sister does not buy food to make meals. She buys premade meals which my mom doesn’t eat because again my sister won’t make them for her. Mom has gone weeks without showering and months without brushing her teeth. She rarely takes her to the doctor and in the last year mom was diagnosed with dementia. My sister has left for days leaving my mom alone and not letting me know so I could check on her. She rarely interacts with my mom and over the last few months has gotten my mom’s credit card terms changed so she could use it for “emergencies” and changed the password so I cannot see the transactions on the credit card. I’ve finally had enough so I begin looking into my moms bank account and see that over the last 6 years my sister has completely drained my moms account every month. First 4 years she was taking $500 per month of which my mom has seem only $3000 of ($19500 which clearly my sister kept and used). The last 2 years she claims she needs all of my moms monthly funds for rent, food, utilities and living expenses. But 2 weeks ago she used moms bank card to get her own nails done. 2 days ago she tried to use the bank card at a restaurant while on a date but the card declined because she drains the account completely. Going back 2 years there have been charges here and there that are not for rent, utilities etc but for my sisters own personal use.

I confronted my sister very strongly today and she refuses to take any responsibility. My mom is on a very low fixed income and my sister earns well over $130,000 a year. She’s clearly taking financial advantage of my mom but my mom defends her actions. I know if my mom was not suffering from dementia she would not allow this behavior from my sister.

Please help. I don’t know how to protect my mom from my sister who is not only neglectful but also financially abusing our mom. My sister has now locked me out of all of moms accounts.