Did yall have an agreement that she would pay you back? I hope you did. If not I doubt she will take the bill very well. That said, I would give her the bill if she continues to turn down the money. No reason to put money into something that will end up being wasted if she does not start taking proper care when she gets them back.

You may try offering less and less and explain the reason you are offering less is because you are putting money into them so you feel the payment is being eaten up by your care. That way she will have an idea that you are wanting your money back without being blindsided by a bill.