My mom used homeopathic medicine under her tongue and now her frenulum has strange swelling and white spots. ?

Very unusual but...: I've given thousands of patients homeopathic medicines for over 30 years and have never heard of anyone having a reaction like this. I'm curious exactly what medicine she took. Most homeopathic medicines are very dilute substances in a carrier of lactose (milk sugar). It's possible your mom is sensitive to lactose- while very unusual, that seems more likely than a reaction to the medicine itself.