How do I tell my disabled friend im not her carer?

THis sounds an awful thread to be making. I have a friend who suffers from chronic pain syndrome and muscle wastage so shes wheelchair bound she has a feeding tube and hasn't eaten In about 4/5 years. Shes recently moved into her own flat with a nurse living with her. I love her to bits she doesn't have many friends and nobody could really be bothered to make the effort with her. I use to go round to her atlest 3/4 times a week and spend a couple of hours there id buy her gifts introduce her to my friends from uni, show her photos etc always being there for her. Recently though I feel like shes taking a bit of advantage. For instance the last 3 times ive gone to see her we've arranged a time in advance say 3pm when I got to her flat nobody I answered I called and she said she was out and busy (carers took her to the shops) could I just hang on. I ended up waiting over 2 hours for her to turn up just stood outside her flat and not once did I even get an apology. Last time she did this I told her I had to leave as I couldn't wait around and she got very moody with me and tried to guilt trip me. Ive also got to her flat when I phoned or text her she would reply she was to busy to see me and I needed to go home although its a 30 minute drive to her flat, I always feel she could have text me that morning instead of letting me drive there. Our friend is having a party in London next month its a 21st there will be lots of drinking and its lots of people I don't know. She said that shes coming and that she wants me to look after her. I do not mind looking after her one bit and as awful as it sounds its going to ruin my night. Last time I took her out she needed her medicines injected into her tubes every 15 minutes, she was crying saying she was in pain and she wanted to leave as soon as we got there but expected me to carry her inject her medication and look after her all night yet I never once got a thankyou. I am not medically trained at all I wouldn't know what to do in an emergency I also have health problems myself yet when I said I wasn't sure if I wanted the responsibility of looking after her on anight out she claimed I didn't care I was a bad friend. Non of my other friends make any effort with her or look after her and I just feel like im slightly being taken advantage of, she always asks me to buy her stuff and never pays me back etc. I know shes ill and that's why I don't know how to handle this situation without upsetting her.

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