When she ask for her for her money, he always makes an excuse and won't give her what she needs. If she wants something to eat he won't give her the money so she can get it. Can he do this? She has been asking for her bank statement and he still denies her.
Regardless, his refusal to provide bank statements is an abuse of power, unless he has a valid reason. However, it seems as though he's overacting, especially in refusing to give her money and possibly providing the necessities she needs.
Goofy, my first question, though, is how in the world did this start? Who prepared the document that authorized him to act? What are the medical conditions she faces? All these are critical to the kind of proxy (someone appointed to act) that is appropriate to her needs.
More information on her situation would help, but based on what you've written, he's overstepping boundaries, abusing his power, and is subject to removal. She would have to create a new POA, and it should be prepared by an attorney so she can discuss how it can meet her specific needs.
If done that way, the previous document would become null and void; that's standard language when a new document replaces an existing one. The attorney could notify brother in writing and advise that he no longer has any authority to act, as well as demanding that he return documents, funds, etc.
He cannot keep her away from her SS even if he is set up as payee. He needs to acct for every penny. And its against the law to use someone else's SS for yourself.