These sites will probably help you determine if you have a mite problem or not better than anything I can say.
Ohio State Mites and Lice
http://ohioline.osu.edu/vme-fact/0018.html
West Virginia Mites and Lice
http://www.wvu.edu/~exten/infores/pubs/livepoul/pfs23.pdf
Congratulations!
Check her for mites, especially roost mites. Broody hens are really vulnerable to them and they can drag down their health or even kill them. They are active at night so you need to check for them after dark.