I understand the venting. I dont think you're being selfish about it at all. You miss your mom and you want her here for your birthday. That's not selfish, I think that's a pretty normal feeling.

I miss my grandmother. She died a day or two before my birthday. I wish she hadnt died so close to my birthday because now I feel sad on my birthday every year. (she died on her daughter's birthday, so my aunt probably feels worse than I do every year)