Dietary tea, is it safe?

My mother and I like to work out together, her more than I sometimes. I think her problem is dealing with getting older,getting a bit self-conscious you know? Recently she bought a thirty day supply of dieters tea, she drinks a gl once a day. Point is it's been giving her diarrhea like every time she drinks it. Is that ok? Also one of it's active ingredients is senna leaves and those just don't sound healthy. Are they?