Of my three children, one always remembers and sends a card for every occasion, one sometimes sends one and sometimes doesn't, the third never. I am on very good terms with all of them, and it is a standing joke with the non-sending one that she always forgets.
I send cards most of the time, but I do sometimes miss out. No-one seems to be all that bothered about it.
Next time you speak to her, make a joke of her not sending - she was probably busy with her own life, and, let's face it, your birthday is less important to her than it is to you. Don't get into a strop over it and make it an occasion to stop sending to her, or to complain that you are neglected and lonely because of it. Do you really want her to remember your birthday because if she doesn't you will stop remembering hers? A "duty" card has very little value, and