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If she deeds her interest in the property to him, she's giving up all rights and there are no legal guarantees that he'll deed anything back to her.
Bear in mind that, legally, she doesn't have to be on the loan paperwork to be on the deed. However, the lender would probably require her to sign the loan docs if she's on the deed.
The only way to make sure her ownership is preserved is to stay on the deed.