Stress does strange thing to the body. Especially if she is bearing the brunt on her own.
Maybe help her out. You are old enough to do so. Think of what you can do to relieve some of her burden, and go for it.
I know many people whom the stress has this effect on them too.. i've never known why but i think you don't have to worry, it's normal and happens to many people
That's tough. She has to seek help, stress is a killer too, ages you too.
Because she drinks too much.
Eating disorder maybe perhaps one in the past. bulimia is hard to get over.
Over-stressed maybe. Tell me about the foods she eats. There may be a problem. Is she sick?
And don't panic, I'm just wondering why, too. It's not a concerning problem yet, so keep calm, even though you should no matter what anyway.