Re: gastric bypass does it stop you from having an appetite?
There's a huge difference between gastric bypass (what your sister had) and a lap band. You say she had gastric bypass but the answer from weighttogo addresses someone who has had their stomach banded.
If she had the bypass, yes it absolutely stops a person from having an appetite. In addition to essentially disconnecting the stomach and rerouting the digestive system, they cut a major band of nerves that trigger the impulse to experience hunger. Once those nerves are cut, the impulse for hunger can't transmit to the brain.
How long has it been since she had surgery? If it's been more than a couple of months, she should be able to eat about 1/2 cup of soft foods pretty easy. Something like cottage cheese and peaches. I would assume that if she is drinking to get drunk, she is outside of the two month window. Assuming that, she really needs to be getting with her doctor to learn what's wrong. Within 6 months my friend who had this surgery was able to eat a small plate of food several times a day.
If she were in the first few weeks after surgery, this can be "undone". The stomach is left in the body and can be reattached. But the longer it lays there unused, it will atrophy and then become unuseful.
Regarding the drinking, I've seen shows where a lot of people who have the bypass become problem drinkers. She has not learned how to cope with not being able to eat as an emotional release so she's switched to booze. The problem is that it goes straight into her bloodstream (because she basically has no full digestive system) and it makes the impact of the alcohol much stronger.
The big answer here is that she should NOT be experiencing the level of physical pain she seems to be in. Why is she not getting help from the doctors? If she had this done in any sort of professional setting 1) she should know the answers to all of your questions. They require all sorts of education/seminars/councilling at almost all reputable places that do this surgery. And 2) There should be follow up care to the 1 year point. After the first few months it's not real frequent, but if she's had these issues from day one, something is very wrong that either no one is listening or she's not talking.
If I were you I'd push to go with her on an appt. to the facility that did the surgery. Also, all of the places (that I know of) who do these surgeries have free seminars for those considering the surgery. You could sign up and attend one for your own information so you know exactly what the story is. I've gone to two of them in considering myself whether to have surgery and what you are saying does not sound good.