Perhaps instead of phrasing in a way where it seems like you are asking for an apology or excuse... You could phrase it so you could get ideas from her on how to deal with this and other disappointments.

You could say you were hurt that she didn't remember to send the card.... And that it has happened in the past and you were upset then too... How should I handle this in future?

Should I change my expectations of you? Should I tell you not to send a card or photos so I will know for sure I won't receive one? What is an emotionally healthy way to handle this? This is a situation that plays out multiple times in friendships and other relationships.

Maybe you could learn how to handle this situation with her and use IRL too.