Small scabs that are itchy are usually a feature of a skin condition called 'military dermatitis'. While there are a few potential causes (including mites, bacterial infections and allergies) the most common cause by far would be a flea allergy reaction.
In my experience, about 95% of cats I see with this condition who are itchy will have a flea allergy.
It is actually very difficult to rule out fleas as we often don't see any because the cat grooms them off. A cat who goes outdoors will be exposed to fleas and one may simply jump on, bite and jump off, causing the reaction she is experiencing.
It is vital she is up to date with a strong parasite prevention that covers against fleas, mites and lice such as Advocate. Owners commonly use parasite prevention bought from supermarkets that are simply not strong enough to eliminate all external parasites.
At the same time, use a strong anti parasite spray in all the rooms to eliminate any eggs/larvae etc. Indorex is a good one.
Any other cats or dogs must also be treated.
As well as this, we must stop the itch scratch cycle and this is best done by getting some prescription anti itch medicine such as corticosteroids from the vet.
If there is any sign of a skin infection (red skin, ooze, bad smell), antibiotics will also be needed.
If we rule out parasites and the issue persists, we need to look for another cause as mentioned above. This can be trickier but can include things like hypoallergenic food trials, strong antibiotic courses etc. At this point it is usually worth running some tests such as a skin pluck and culture.
However, the vast majority of cats react very favourable to an anti parasite treatment and some anti itch medicine.