she may be allergic to the food. or maybe she's eating too much? does she roam the neighborhood looking for handouts?
if its only been going on for a week, I'd call my vet if I were you. it could be serious.
She eats about the same as she always has.
And she only goes outside to go to the bathroom, in a gated backyard, so she doesn't roam the neighborhood.
And she's going in on monday.
Perhaps she has too much at each meal. How about dividing her food into smaller portions. Her stomach may be overloaded and so she has to get rid of excess.