When your children break people's things

So here's the story, my mother in law was over playing with my 1 year old and I told her "don't let her play with your sunglasses she will break them" 
They are some kind of expensive brand. Anyway, she later gives my daughter the sunglasses and of course my daughter breaks them. I said to her I told you so, and she said to my daughter (directing at me) now your going to send your mummy bankrupt because she has to buy grandma a new pair of glasses. I said no I don't * laughed* I told you not to give them to her, she said but your daughter broke them when your daughter brakes other people's things you have to replace it,
Now it's become a heated debate I refuse to pay for it ONLY because I warned her and told her not to give them to my daughter!
What do you think?
This sunglasses are $350