She's just been spayed 2 weeks ago, has had 2 different types of food,I've introduced her to a new food but she has diorhea now.what shall I do?

How did you introduce the new food?
You should gradually introduce it, i.e. adding a bit of the new food to the old food and gradually increase the new food over about 10 days or 2 weeks until it's just the new stuff. Otherwise they may get diarrhea.