Legally, you have to pay her--the fact that she may owe you money, or committed some crime, does not absolve you of that responsibility. Your proper recourse is to sue her for the money she owes you, not to withhold her pay. If she chooses and can document that she did the work, she could potentially sue you for the unpaid wages. Of course, depending on how much she is owed, whether she wants to bring that kind of attention, etc., she may not due so--but from what you write, she would have the right to do this. If she does sue you for the money, you could counterclaim for the amount she stole, though you would need to be able to prove that she stole it by a "preponderance of the evidence"--i.e., that it is more likely than not that she did steal.