Hi, welcome to BYC!
I agree it SOUNDS like broody... but I also have never seen it happen when coming into lay. But after laying a few eggs, OH ya. Doesn't mean it can't though. The more chickens I have, the more things I see, the less surprises me! Breed can play a role in how broody a hen will be.
I would try to break her from being broody. Kick her out of the box a bunch of times. I use a dog kennel with a wire bottom I put in place of the tray and elevate it a little with NO bedding so there is nothing to nest in. Some girls will break in 1 day, others will take a week. Either way, broody isn't good for a still growing girl.
I however would not jump to conclusions but pay attention to the signs. When you remove her from the box does she immediately run back to it? Or does she stand around and pump her tail like she needs to poo? Is she puffed up or does she make a cluck sound? When you sit her down does she stay in that position for a moment before getting up?
Easiest time to see parasite is after they have gone to roost, couple hours after dark... go in with a flash light, keep it dim so everybody stays on roost. Take them off one by one and hold them on their back with legs bent towards chest quickly part feathers near the vent and look for anything running away, do the same to the abdomen. If you do see something, my suggestion is a permethrin based spray because it's easy to use, effective, affordable, and requires no withdrawal time for eggs if used according to directions. There are organic versions (spinosad & others), but were not on my radar or in my price range back when I first started.. and I'm going to use what I have.
Good luck!
