Hmm....
Well, I rarely send cards... I look at the cost, and the fact that most of the time they end up in the trash... money is VERY tight for us right now.
I used to call my M. a lot, but don't call as much anymore.... it is harder for her to understand much on the phone now, and I don't want to disturb her if she is sleeping. (She is 88 now...)
I don't know if this makes a difference, but I am 54.....
My kids don't send cards, either....... they call, but not often. I do talk to 3 of them on the internet frequently, though.... (one of the 4 still lives with us, so I see him when our paths cross... he works almost full time AND goes to school, so he isn't home much.)
Rather than focus on what she ISN'T doing, focus on the positive things.... she did give you and your husband a party for your 50th... that is a big accomplishment!
Frankly, as far as the issue of the birthday card vs the phone call, I think the fact that she DID call you on your birthday was her way of greeting you... and you chose to be petty about the point a week later that she didn't SEND you a card...... so, yes, she is hurt by it... she reached out to you, and you rejected her gesture.... she probably feels that if she does call you, that you are going to go on and on about why she doesn't call......
As you said, she is an adult... she has a life now, also. It is sometimes hard for us to understand that they have things they need to do outside of our life.
I will admit, though... you sound rather demanding... and that may be why she chooses not to talk to you? That is one issue with my SIL and his mother.... she gets very demanding that they spend time with her, and so as a result, they don't WANT to spend time with them.
I would suggest sending her a card, apologizing for your comments, and tell her that you will be gone for a month, so she knows where you are.