Force-brushing her is just going to make her more disturbed and upset by brushing. (And I hope you had her with her feet on the ground while holding her neck; some cat owners don’t realize that you cannot hold an adult cat up by their neck skin without the potential of extreme cat damage occurring.) She’s freaking out, the brush is still there, the brush gets associated with the ‘freaked out’ emotional state, so next time she sees a brush she remembers how freaked she was, and gets even more freaked, etc.
First thing first is to figure out what her flakey skin is. It might be a mild allergy, some parasite, or just sensitive skin, but it’s likely treatable. Get her to a vet and see what he recommends. When her skin doesn’t hurt (assuming that was the root cause) she should be much more groomable. At that point you will probably need to re-introduce her to brushes.
This will involve leaving the brush in an obvious place, like the middle of the floor, away from food dishes, water dishes, toys, bathroom areas (it might be trying to eat her food!
), but where she’ll notice it. If you see her looking at it, but not fluffing up or growling or giving it really angry ears, praise her in your customary fashion (pats, an extra food nibble, whatever). If she goes toward it willingly, praise her extra. Eventually step up to holding it in one hand, away from her, while praising her with a nibble or pats, then eventually to touching her with it, just once, not a brush…just a tap. More praise. Then start up on grooming say, for 10 seconds, or five strokes or whatever. Praise praise praise.
Whenever she seems to not care about a certain stage, with no apprehension, bump it up to the next stage. If she gets too freaky, pull it back a stage for a few days.
She may have no brush issues, but she’s probably associated brushing with pain and fear and loathing by now, but that’s not permanent; it just requires some patience. Even if you do get her shaved by a vet, which is nice in hot summers, having her not have a fear of brushes is a good thing, as you never know when you might need to give her a quick brushing and only have a normal one available.
(I’m having to get my chihuahua re-used to baths right now. Somehow walking around in heavy rain is great, but just getting your feetpads wet by a wet paper towel is the most cruel thing imaginable to him.)