Hi Lily,
Congrats on your new kitty 🙂 I recently was in a very similar situation — have had my Celeste for two weeks now and she was also about the same age when I found her.
She was eating fine but had the same bathroom issue as yours. It took her a few days to pass a stool and I think it may have been slightly stress related because of a change to her environment. They also can take a few days to get things “moving” again after they’re taken in, fed and given medication/dewormer. Give her a few days. Celeste took about 3 days to pass a stool, but she finally did! I would say if after the end of 3 days if she still hasn’t gone, give the vet a call, but no need for alarm yet.
As for the food, have you tried different kinds? Maybe she’s just being finicky. It’s good she is eating when shown, but I would try mixing it up a bit. My kitten loves chicken patte and salmon — I feed her Natural Balance for kittens and Wellness core (also for kittens). She enjoys both of them a lot. I also second kittyzee’s advice; try mixing it with a little bit of formula. Also, kittens sometimes take a bit to get used to a bowl, so maybe try putting the food on flat saucer or paper plate; not as daunting to a tiny kitten. She will catch on quickly, don’t worry!
Make sure to give her lots of cuddles and make her feel loved / safe, and she will pick up on things and adjust remarkably quickly. You’re doing everything right by getting her vet care and feeding her and watching her bowel movements, etc.