Can I take legal action against my late mother's POA?

My mother, 83 yrs old, had several heart attacks last year and a stroke which left her disabled. She lived in Houston, in her own home and had 2 adult children living close by. I live in Louisiana, in which she was coming to live with me, but had the attack a few days before the move. My sister, had the power of attorney and she took my mother and hid her out from care center to care center so we couldn't find her. When my mother died, she didn't even contact anyone, not even her grandchildren or her best friend. She died without all her family, except my sister. I found out she died by googling her name. She had past 2-1/2 months prior to the time I found out. I contacted the rest of the family and told them. Everyone is so upset for not being there when she died. Is there any legal action we can take for what she has done to the family? This was a cruel and inconsiderate thing she has done to everyone. She won't return our calls or emails. We also think she has taken all Mom's assets and has hidden them. We don't know what to do. Please help.