Pissed off and upset with unreasonable people

I am just needing to rant and any advice on how to get out of this would also be great! Basically my friend from secondary school turned 19 today and has announced just now that tomorrow she has decided for her birthday she wants to go to London clubbing and for dinner and stay in a hotel then spend the next day out in London. I said ages ago I would go to her birthday thing and now suddenly she has turned around and said she is now going out in london and everyone apart from me and this other girl has let her down etc etc. I don't want to upset her or for her to have a **** birthday it's just it is now just so expensive and I can't afford it. I have tried to dissuade her from going up to London but she really really wants to and won't listen. Neither her or this other girl (who I havent seen for 3 years and barely know) have been out in London either. I have now spent about 2 hrs trying not to argue with her but the whole thing just keeps getting more and more expensive! I have known this girl for nearly 8 years and I dont want to let her down but at the same time 1) it's too expensive 2) I have been ill for the last week or so (I even cancelled going out last night) and I just don't have the energy

I dont want to tell her I cant afford to go cos she is sooo looking forward to it now. She said when I mentioned maybe going somewhere else that she only wants to go to London or nowhere at all.

I dont want to tell her I cant afford to go cos she is sooo looking forward to it now. She said when I mentioned maybe going somewhere else that she only wants to go to London or nowhere at all.

Anything other than you can't afford it will make it alot worse than it is.

Thanks for the replies. I agree with you that she probably is spoilt and we've fallen out before because of similar things she says and does but I just don't want to argue. I will phone her in a bit and try again to talk to her and if not I suppose I will just have to budget!