Give her some diatomaceous earth/fullers earth to add to their dust bath. It's available at pet stores that sell fish. Then get a chicken safe insecticide that takes care of fleas, mites, and lice. Use it on the birds and move them to a quarantine area. Treat them again when the directions on the insecticide say it's safe to do so. They'll need to be quarantined from your flock while being treated. No sharing space, feeders, waterers or the same ranging area. If you quarantine them in their old home you'll need to spray roosts and clean as best you can. Wash your hands thoroughly before and after handling any of the birds. Before combining the flocks carefully examine all birds in both flocks. Wash thoroughly between the two flocks. If you see anything concerning delay the merge until you know what you're seeing.
And maybe think about whether you really want those birds. Even if chicken; math doesn't make you count them they're going to create more work and cost for feed. Unless you like the chickens you're just doing your neighbor a favor by taking them off her hands. If I were you I probably wouldn't add them to my flock health concerns, neighbor drama, and if they were great chickens would she really be giving them away?
