My mother has been living with my younger sister for 16 years and just found out they have been robbing her checking and her savings is gone.

I love and trusted my sister and her husband but found out they have stolen all of my mothers money for the past 16 years, except for a trust account which has me and my sister's name on it. But she has stolen way more than her half. She also has a credit card in my mothers name that is maxed out. Charged vacations. computers, gas, haircuts etc... to the tune of $14,000. and was paying the minimum every month from my mothers checking account.
She is in a home since Aug and I hired her elder care lawyer to get her on medicaid, she just got approved. But from Aug till January the bill is $53, 000. and the home is trying to get me to pay half. Over the course of the 16 years I calculate my sister took over $300,000. dollars and doesn't admit to any of it.
I see this as credit card fraud and elder financial abuse.
I'm out of work and need some legal help here.
One other thing is my mother has no clue what's been done to her.
Do i tell her?