With a few more of the blanks filled in, it seems like it would be important to get here back to her core diet before any of the weight loss. Regardless of whether it was kibble, canned, kitten or adult food, just get her back on her previous diet.
New food introductions shouldn't be made abruptly especially with kittens. New foods should be inserted in about 10-20% increments over 2-3 weeks. This gives your kitten the opportunity to make some digestive adjustments and also gives you the opportunity to keep an eye on what's coming out the other end.
You can also introduce the new foods in treat size portions, not more than a tablespoon along with their standard food. This will point out if they simply have an aversion to it. My cats all have things they don't like to eat and they can all be pretty obstinate about what they don't want to eat. None of them like turkey, one of them doesn't like rabbit, another one doesn't like duck and yet another one doesn't like the normal quantity of fish oil in their raw food.
It can definitely be a challenge, and if you change multiple things at once hard to find the culprit. As your kitten isn't experiencing constipation I would get the pumpkin out of the diet until such a time that you find greater need. My older cats, one of which has the need for a lower protein diet had some big issues with pumpkin which took a long time to transition in. We had better luck with well cooked peas pureed in a food processor. The pumpkin definitely took the better part of a month to transition in and I was relieved when we didn't have to be a scientist to mix their individual foods to get them to eat at their normal rates.