I think she thought of you on your birthday and wanted you to know she was thinking of you. Sometimes we can sit and ponder these situations and there are no clear cut defined answers. We just have to accept them and move on. You can send yourself over the edge if you keep trying to figure out something that at this time, there are just no real defined answers for.
You have done your job in sending a card to her. You were thinking of her and you let her know that. There can be many different reasons for her not responding to you and for you to assume what they may be is not doing you any good hon. Unless you live her life, you just can't know what's going on in her mind and her life.
Be well Impala......know you have done what you can and let this go for now. Give yourself a much deserved break from all the questions and uncertainty. Maybe in time you will find the answers you so crave, but until then, put your energies into taking good care of YOU! You so deserve it

sabby