@Halima19 It was responsible of you to follow Airbnb protocol, which is indeed to first notify the host to give them an opportunity to address the issue.
But I'm not sure what you expected her to do or say at that point- you had already left and didn't want to return. I suppose she could have said she was sorry that you got freaked out by the mouse, but it isn't her fault that there are mice in the area. It's not like she forgot to clean or purposely put a mouse in the house.
If you had just called her when the mouse appeared, maybe she would have offered to bring over a trap or something. But you had already vacated, so what more could she do than say to deal with Airbnb for a refund? What sort of solution did you expect her to offer?
FYI hosts do not get paid until at least 24 hours after a guest checks in. Until then, Airbnb has your money, not the host.
When the host doesn't offer an acceptable solution, then the next step is for you to cancel, and let Airbnb know what the issue was and in most cases you'll be refunded.
Some hosts just consider it easier not to engage with the guest about complaints, if it's a complaint about something that nothing can be done about and it's obvious that all the guest wants at that point is a refund.
I happen to live in the tropics, where insect life is prolific. First of all, I think guests should do a bit of research into what to expect, in general, when booking in an unfamiliar area. If my guests demanded a refund because they saw some ants, a beetle, a cockroach, a spider, or any one of a thousand other bugs, I wouldn't be able to host. But I do let my guests know to expect these things- of course I clean their room thoroughly, but any insect can come in again. It's just a fact of life here, whether you rent a $500/night beachfront place or my countryside $30/ night private room. (I do have a mosquito net so guests won't get bothered by anything while they're in bed)