Can I legally take money for my mother's share of expenses out of her next social security check?

My mother is 94, has demensia, and named me durable poa in 2009 when she was competant. I am 71. We both have small ss checks, and I had to rent an apartment for us. It takes both checks to live.I have a sister who always wants to know where does the money go. I have become unable to care for her, so my sister took her this week. I now can no longer afford to pay the rent. Can I take her share of expenses out of her next check so I can give a 30 day notice.