Need help; I'm totally clueless!

dlb823, thank you for your suggestions. When I was younger I do remember she did eventually get help for her mental problems and was put on some medications that helped. The only problem was that once she felt better (and during that time, she's had dramatically changed her behavior for the best), she thought she could stop the medication because she was well enough, that it might have just been a phase... but as my father and I know, she's always acting like a bully to anyone and at the beginning of her illness she negatively took advantage of that.

37Antiques, I definitely agree with you... She had one of the best oncologists we know of... I don't know if he's well-known, but he wrote the book "so you failed your breast exam"... He was a very generous and comforting doctor, and the center she went to was filled with very kind-hearted people.
She's always been know to be late to all of her appointments, so the head nurse would either call me or my dad to see if she was coming, but I guess her behaviour was unacceptable and was pretty much unreliable so they had her sign a waiver. But I think when my parents discussed this after the fact, she said that one of the treatment had to be stopped early because they had noticed signs that her heart was getting worse. When my dad had met with one of the doctors, they had mentioned that if the cancer came back, she would not be able to get any kind of chemotherapy or radiation, but at that time her cancer had gone away for the time being, but she had a 60% chance of it coming back within two years and it was extremely agressive.
After she stopped answering any of the hospital's phone calls, for a while, my dad had stayed in contact with the head nurse that was very worried for her and said if she didn't get it checked, that there could be nothing left to do. but that they had done another exam that showed more cancerous cells in her other breast. The reason why he had stopped talking to her about how my mum was doing was because she had called the nurse personally and scolded her for talking to him.... so that to me kind of tells me that there's something more that is going on here... alongside the cancer... and the nurse was very worried about her.  
The last appointment she had gone to, the one that lasted only a few minutes, she had only seen her PCP that she has seen for a long time; my guess is that visit was only to get a signature and to pick up a triplicate Rx for the pharmacy... I don't even know if she physically even saw the physician.
She does have other physical problems. Even though she is very young, she has been taking more pain medications than the amount that was offered and prescribed for her, for her joints for as long as I remember. She has always made unhealthy choices, and, having an auto-immune disease as well as organ failure, I know what it feels like to be very sick and not even be able to get up... but I also know that it's very important to eat healthy foods, try to at least walk a little bit and stay positive... but she does none of that... She doesn't talk to my sister... she stopped talking to my dad...
I praying so hard for the courage to talk to her and tell her that it not only hurts her, but it hurts this whole family...
could you tell me what the other symptoms are that it could possibly be? Maybe there's something my dad can do or say to one of the staff at the clinic if we had an idea of what it was...

thank you so very much for responding to my post.... I pray that the cancer won't be a problem anymore.... I feel really blessed to have seen this site and see how much support and strength everyone has.

Those are really good ideas.. I don'tknow much because I only get my information from my dad, and only see her every now and then.. it's sort of hard to explain. But it seems like most of the time, she eats and drinks something, and within a little while... anywhere from 10-45 minutes. She'll spend countless minutes vomitting what she had just taken in. She is very pale, and hardly uses the bathroom. It seems like she has been in pain more often nowadays, like cramping pains.. and since she's taking so much medication to maybe mask symptoms of something more serious, it makes me and my dad more worried because the pain is so bad that the medication isn't helping anymore. but she does take a lot of advil, acetamitaphen, muscles relaxers, vicodin, dilaudid, and fentanyl, which, I know taking the vicodin for as long as she has been has not helped her liver *at all*.
She is pretty pale, really gray, and can hardly stand up. very tired all the time. and sleeps more than usual. And has been sleeping MORE than that lately. Everything has gotten a lot worse in the past couple of weeks. She is pretty bloated, I think, from my experience with kidney problems, that as much as she is drinking, that she should be urinating more than she is. but usually we only notice her going to the bathroom *maybe* once or twice a day.... if that.
How can you tell if someone has jaundice, like yellow-colored nails, eyes, maybe skin, right? or do I have that confused with something else?
Oh yeah! My dad and I have been thinking about how, if it were possible to have her taken to be cared for in a full-staffed medical facility... but we don't really know how to go about doing it and even if it were possible, how to convince her that that would be the best option posible, for her as well as the entire family.
Thank you so much for your guidance. You've been a really big help... I really appreciate your ideas... it's always better to have fresh eyes when it comes to these sort of things... It means a lot to me to have help like this...