Hi Jane,
If I may share my opinion, even though I don’t know you or your daughter… It sounds to me like your daughter’s behavior has changed and that is more the issue than a birthday card and not following through with a promise to get together.
You talked about her boyfriend and that signaled an alarm for me, the relationship with the boyfriend may be part of the real issue here. Is he changing her? Is she changing because of him? Is he controlling? What is going on with your once close relationship with your daughter?
This concerns me too. I have had it happen with friends. It is cause for concern. If a partner (boyfriend, spouse, etc.) is a healthy match they will be supportive of their loved ones relationship with anyone who is positive and makes them healthy (in this case you).
My only suggestion is to bring it up to her as positively as you can. Are you concerned she might become angry with you and cut off communications? That may happen, but if you do it from a place of love and support instead of hurt about how she was not considerate toward you it may help you both.

– Chris