Should I still do the flea treatment?

Most flea treatments are TOXIC!! The only thing you need to kill fleas and ticks is called DIATOMACEOUS EARTH(Food Grade only). Google for more info. It's a shame that vets don't tell their clients about this because it would cut into their profits bigtime. DE is safe, natural, effective and inexpensive.

It really depends on what you use for flea prevention. They all have the possibility to irritate the skin, but some such as fipronil (Frontline) and imidacloprimide (Advantage) are much easier on the skin than harsh things like Hartz and BioSpot.

Also, it depends on whether your cat is indoor or outdoor. If your cat goes outside, then you should definitely continue with the flea prevention if you don't want to risk an infestation. If she gets fleas and starts stressing and itching it will make her dander worse

Topical flea treatments usually do not dry out skin, so she should be OK. I would just make sure that there are no open scratches or sores right where you apply it, because it sounds like she might be scratching where her skin is dry.

your cats dandruff may be down to needing more Vitamin A her diet try dry cat food with vitamins

i would say not to to do the spot-on treatment on till talk to your vet.

does she have fleas right now? if not, i would skip it until talking to the vet.