What's the problem with a renter offering to settle for a 'used' vanity top?! Did you go down there and inspect it? If it's brand-new, then you're right. The Renter can offer nothing and still lose the ENTIRE replacement cost from the damage deposit (IF there is one.) If I was down there, facing the possibility of having to fork out several hundred dollars, I TOO, would try to negotiate the bill. Heck, the 2 ladies might be able to argue that the top ISN'T brand-new due to noticible, previous damage. Then again, the landlord may produce a receipt showing the countertop is a week old. NOT YOUR CALL, X-GUY!
Sure she can be sued. And give these ladies some credit for pointing the problem out, and owning up to their 'mistake' which is a lesson YOU should take. Are you an attorney now?! Go Soak Your Head !!!
Sorry, ladies, for the intrusion. X-Guy is an 'too long of a story to get into'. Do what you can to work out the 'problem' with the landlord. As Jim says, don't attempt ANY repairs yourself. IF you leave any $$$ with ANYONE, landlord or not, make sure you get something in writing that you're leaving $$$ with XYZ person for the use of replacing the countertop, cost and labor. Take a picture of the 'guy/gal' you give the $$$ to. (One lady give the $$$, the other snap off a quick picture of the receiver's face. Take 2 and make sure you get him/her looking at ya. And have them sign something too!!!)
I commend you ladies for doing what you're doing. That goes a long way. My best to ya and hope this helps.