Hair growth problem

My 7-months old foster kitten was spayed over three weeks ago and she got a little bit of fuzzy hair growth at first but after that she has not had any additional fur grow in. It didn't worry me too much at first - actually I didn't even think much about it (I've had a lot going on lately) - but the last couple of days I also noticed that on her back, right by her tail, her fur is shorter, like it's been cut very short, and there is also a small bald patch. Last night while looking through all of her I also noticed a small bald patch on her shoulder area. I can't tell for sure but it also feels like the fur on her head has changed texture and is thinner. It's very odd and throughout the years with many ill foster cats I've never seen anything like it. I don't think it's ringworm or mange as it doesn't look like it. If it was only the bald spots I wouldn't be so worried but with the lack of hair growth on her stomach I'm really worried that she's seriously ill.

Other than the hair issue she shows no sign of being sick. She eats well and plays like it's going out of style. In fact, the past couple of weeks she's been better than ever before and it seemed like she's finally recovered from the aftermath of an injury she had when she came.

Does anyone have any idea what could cause these symptoms?

(She will go to the vet after the weekend but I thought I'd check here too.)

Do you have fleas where you live?  Have you noticed her biting/chewing on her fur?  It could be something like allergies too.  I would take her to a vet to see what's going on with her hair.

I don't think it's fleas or a flea allergy. That could explain the bald spots but not the lack of hair growth on her stomach. Her belly is almost as bald as it was the day after she was spayed. That's what worries me the most. Could allergies cause hair not to come back after it's been shaved?