"DO NOT attempt to have the vanity replaced yourself. It will cost you more money than you are liable for here, and it shouldn't be replaced for cosmetic reasons alone if the place is a rental."
It is clear that you know little to nothing about the rights of a landlord and rental property on general not to mention the responsibility of a renter. I own rental property. What she did, accident or not, she IS COMPLETELY LIABLE for. What happened IS NOT considered normal wear and tear. It is a clear cut case of complete responsibility on her part for the ENTIRE COST. If her deposit won't cover the damage she CAN BE SUED by the owner for complete recovery. Think before you speak... or in this case KNOW what you are talking about. What he does with the $$ is the owner's business. If she followed your advise she could end up in court.