My sisters account was frozen for the 2nd time. She only has social security going into that account because that is all she has. The bank took out over $500 out of her $800 dollars. Can she recoup the entire amount?

She can recoup on the money that was SSI if she can prove it in court, and if it was the IRS or the government garnishing that, she won't get any of it.

She didn't learn from the first time? She needs to file a letter with the bank informing them that the only funds being depositied in that account are exempt frpom garnishment so they should not honor any writs against ythe account.