D.T.
First of all, Happy Birthday! I share a birthday with you (+5 years), as does my twin sister - as does Prince Charles (tangent I know). :o)
I am in the same boat, although my mother calls a little more frequent than 3 times in 11 years. Yikes! My twin sis definitely takes it a little more personally than I do, but I also get a little upset. She usually remembers a few days past and apologizes up and down.
Although I haven't done it in a few years because money has been thin for us the past few years, I used to send HER flowers on my birthday as a thank you for giving birth to me! After all, she did all the hard work. She LOVED receiving the flowers and didn't forget to call then!!
So have I given you any good advice here? No, but just know that you're not alone and that you certainly have the right to say something to her. It might change things and it might not! What do you have to lose? ;o)