I am just sorting this out.
First of all I have to admit that I too had been wrong. That I did not decline the invitation amiably, but instead created cause for an argument. It almost looked like I started this argument intentionally, which should never have been.
On the other hand, I think it is only natural that I should feel uncomfortable, when this friend expects me to celebrate her own birthday, while forgetting all about my birthday which is only a few days earlier than hers. On the eve of my birthday, she sent me a sms just to ask me to confirm whether I am going to her birthday party, without even saying happy birthday in return. It is absolutely ok that people forget other people’s birthdays, I do that myself sometimes, but when I casually noted to her that I just had my birthday yesterday, she acted as if she heard nothing and continued about her own birthday party.
When I asked who would be in the party, she seemed offended that the guest list should concern me. She thought I would be there just to celebrate her birthday, and the other people would not matter. Which is strange to me in fact, because if I am to give a party, even though I would love to have all the people who matter to be with me, I would still, as a host, consider if these people would also be able to enjoy themselves and feel comfortable in my party.
And so I think, this is about the proportion of give and take in friendship. Anyway I have sorted this out now, and I wish everyone happy birthday and friendship forever.