7 week old kitten is sick!?

I think that you need to gradually change the cat's food from what she was previously used to, to the new cat food you are trying to get her to eat. You need to find out what they were feeding her before and then start off with like 25% of the new food and 75% of the old. Then keep gradually adding the newer food to her. Once she has gotten used to it, she should be ok. I did this with my cat, and she was fine. Unfortunately, cat's get used to what they are fed and you have to introduce newer foods to them in increments or they do not do well with it.