It is possible the answer to your question is in the contract the buyer and seller agreed to. Review the contract to see what is expressed in relation to cancellation and return of earnest money. The contract should spell out remedies for default. The answer below are both part of the puzzle, however there are generally more details than what we have at hand. As indicated below an attorney can help guide you to the best course of action.
Forgive me for asking, but how can you miss the a/c units? Was the offer written, sight unseen?
Unless you have a really nice "seller" and there was some contingency in the contract, your buyer will more than likely lose her deposit.
Any answer on this, without all of the details, is purely speculation.........On the surface, I'm sorry to say, it appears that critical information relative to the property was overlooked. The issue here is who should bear the burden.
I would like to think my customer would have been aware of such an important issue and it was my responsibility to do so........
The "Eckler Team"
Century 21 Almar & Associates
Venice, Fl 34285