@Xinyi8 You say the host didn't inform you that she had cats- are you saying that isn't mentioned anywhere in her listing info?
Regardless of whether you knew beforehand, or whether it's never happened before in other homes with cats, it's just common sense not to leave food out that animals would be attracted to. Even without pets in the home, accessible food left out unrefrigerated or uncovered attracts rodents, cockroaches, etc. I have a cat myself and while she wouldn't be the slightest bit interested in a bowl of fruit, she would certainly try to devour a pastry she could get to.
Personally I find it petty to seek payment for a $12 reusable shopping bag- unless it's some huge hole that things will fall out of, it sounds like it's still serviceable and could easily be patched if it really bothers you.
But if you feel otherwise, you could message the host with a photo of the bag and ask her for payment. I just wonder if you did quite minor and unintentional damage to something fairly inexpensive, if you would be amenable to being charged for it.