I'm going to criticize my friends relationship on her birthday
Does she spend too much time with them?
That is one of the reasons.
I mean, it is her birthday. You should not do anything to upset her on the one day a year that is hers.
What about me and how I feel?
I think you can hold off for a day and focus on her. Why not shower her with love and praise instead, a birthday is supposed to be a great day! You might come to enjoy the whole event.