Salaam,
When it comes to repentance I've never seen anyone (scholar or nonscholar) claim that any sin is beyond the forgiveness of Allah swt. Nothing is beyond his majestic scope. If the woman is al-kitaab then there are no rules stating you cannot marry her.
On a more practical note though, has she been through counseling? Women who've been prostitutes become them usually do an extremely disturbed childhood, sexual assault and/or abuse. So she will need some cognitive therapy to heal whatever lead her to believe she has no value in her body. She also needs to have blood tests for STDs and a pap smear for cervical cancer.
Brother, it speaks highly of anyone willing to look past someone's mistakes and make excuses for them, mashallah.
Wasalaam
~Sarah