Her home, perhaps, but she must spend a lot of money on food and other stuff to care for all those many, many animals. Also, I'm not convinced that she works as a vet, and even pet shop is debatable. She seems to help out with music at official events, too, but over all she doesn't really have a clearly defined job.
Also, it's a tree? Looks like a regular cottage with moss-covered roof. Twilight and Zecora are the only ones who live in trees, I'm pretty sure