My friend told me she has brown stains in her panties in the vaginal area. is that symptoms of starting her period or should she be worried?

Brown = old: Typically, brown blood is just old blood and nothing concerning or a threat to one's health. When it occurs in middle of period, it's called breakthrough bleeding and could be a sign of hormone imbalance, polyp or fibroid. If it keeps happening and friend is concerned a quick trip to gynecologist can solve the question. Good luck!