It could be mites or it could just be dry skin flakes. Is she molting? Is it just dandruff or are there like small centers in the dandruff area that have crusts? (It’s a bit difficult to describe what I mean, but like small white crusts that the bun don’t like it when you pick at or try to comb out). If there are such rustiness it’s likely to be mites. You can try and put some Vaseline/bag balm/ diaper rash cream or other far cream in the dandruff the parts, if it’s just dry skin, it will go away in days.
If it is mites (you’ll notice because it will get worse) you should contact your vet and ask for a prescription for Revolution. It’s super effective against mites. The vet might want to take a sample to see if it really is mites, or you’ll only get the medicine, it’s a safe medicine for bunnies.
Whatever you do, DO NOT use Frontline (fipronil), it can be deadly for rabbits. (Not that you would, but I always like to warn against fipronil for buns since it’s so extremely dangerous).

It’s good you’re keeping an eye! If this is mites, you’ll see more and bigger flakes of dandruff and more itching with time.

It doesn’t hurt to treat with Revolution. If there are mites, then they will be dead. And if not, well no harm done.

As always, I have to say this just in case someone else happens upon this thread. Do not use Frontline on bunnies. Thank you, that concludes this public service announcement.