It is really hard to diagnose anything over the internet, but your cat sounds like she has either a parasitic infection or an allergy (could be allergic to a parasite too)
You need to find out if she has had a skin scrpae to try to rule out mitess, the comb test can often rule out fleas and lice.
However, any itchy animal MUST be treated for fleas effectively and regularly as this is the most common reason for itching in cats (around 70% of itchy cats are flea realted problems IIRC)
And the household must be treated too as much of the flea lifecycle is off the cat, in the household , carpets, cushoins, beds etc.
The cat may well have another parasite, but in all honesty mites are rare in cats,(except ear mites) and more common in dogs. Many of the products vets supply are againts mites too. Don't rely on pet shop stuff, it is often not very effective.
I would definitely NOT recommend you to use randmoly chosen herbal/iol based products on the cat, if the skin is broken this can cause further problems.
She may well be allergic to anything at all, fleas, mites, pollen, house dust mites, some thing in her food...
very difficult to prove and blood tests are often not conclusive.
It really is hard to decide what she has, she probably had some steroids at some point which will control the ithcing but not actually cure the problem I am afraid.
It is very difficult to know what is wrong with the cat even with "tests" as there are no conclusive tests for allergy I am afraid.
it is important to treat the cat vs fleas with stronghold or frontline or advantage, and to treat the environment. A vet may be able to help by presscribing more steroids and helping you to decide if you want to try an "avoidance diet" to see if is a food allergy.
I am sorry not ot be able to say "it is obviously xxxxxx" and there are no simple answers, but until you have a 100% tight flea treatment going on, there isn't much point in considering anything else TBH.