If you have police reports and credit bureau information it should be more than enough to go back to ATT.
Since I don't know what happened I can't speculate why ATT is still holding your wife responsible.
Can you add some details? It might might help in suggesting a next step in getting this fixed.
BTW the weak link is usually the email address. A thief hacks your password and then has access to every account related to the email. iTunes, bill payment, etc. I have 2 step authorization on my yahoo and gmail to prevent any login without a code, sent to my cell phone.