My vet recommended no food for 24 hours, but free access to water for Savannah when she was sick. Then start back with a small amount of either her food or a mix of yogurt and rice. If she holds that down then slowly increase, if she doesn't then remove the food for another 24 hours, after that he recommended to bring her in. Remeber you have no idea what she's been eating before you found her, so it could just be a tummy upset from getting regular, decent meals. Good idea to have the mass checked though.