It's certainly not common for snakes to shed as often as this, but it does happen. Sometimes it's for no apparent reason, other times it can be due to a growth spurt.
I wouldn't be concerned about mites being the cause. A snake would need to be heavily infested with mites for it to shed twice in such a short space of time, and you would have detected the mites before then. Still would be wise to check for mites, though.
Feeding a snake during any stage of shedding isn't bad. It would be wise not feed them while in their milky stage of shedding(but still can be done), but feeding her any time after this is okay.