I can't imagine how stressful dealing with all that is. I think you are like me (since we are twins after all) and like to feel like you need to help everyone and put them ahead of your own problems. In this case though, I definitely agree with what Sinead was saying - you need to take care of yourself first. Being so close to the end you don't want to do anything to screw that up after all this time. I know how it was at finals time when people are freaking out and want your help, but you just have to get to the point where you say no. So even though this situation is a bit different and more complex, I say you deal with it the same way. Just take some time and leave you apartment to get your work done in peace and then you'll be able to get a much better outlook on things.
And definitely try to encourage your friend to get some professional advice. She is very lucky to have you around though.