Thank you for rescuing this pigeon.
Small white flakes is normal for pigeons and falls off when they are grooming.
However, if you see her itching and scratching alot that could be due to lice and mites, especially around the ears.
You can take care of mites and lice with any regular bird mite and lice spray, however, if the bird has blood sucking mites around the ears, you can put a little petrolium jelly on the spot to cover, and the mites will suffocate.
It might be best to use Scatt as it will kill all blood sucking mites, which there may be more of internally as well as externally. Give the bird garlic water to drink and that will also rid the bird of unwanted pests, like worms.
A clove crushed to a gallon water, or human grade garlic soft gel caps, one per day. The garlic has many benefits besides helping rid the bird of pests.