Mystery Smell

I gave a kitten I found, (named Monroe) to my friend Rachael. She has mentioned a weird smell coming from her back end. Rachael is really concerned about cat smells and is obsessed with keeping litterboxes and things sparkling clean. Which is good, but this smell is something that she has asked me about. This just recently started happening, that she noticed the smell. Monroe went into heat about 2 weeks ago when the smell started and she was just spayed last Friday. I am thinking this smell is related to her heat cycle and it will clear up in a week or two when she recovers from the spaying. I am relating it to when you have to give male cats a few weeks to get the hormones out of their system for them to settle down. Am I right? The vet worried her over the phone saying it may be an infection but i don't think she pointed out to the vet that she smelled this starting when the cat first went into heat.

Any thoughts?

possibly anal sacs? I know a couple of mine leak and if you hold them you might get spotted :S If it was infection and she got spayed chances are thety would have noticed during the spay, still possible tho. I noticed my 3 fat cats leak or if one of my guys is upset and you hold them against will(ummm vet trip.... ) If not sure tho worth a quick trip to vet(and if its anal sacs they can express them and it will stop for a bit) RJ