Lol, yes, I'd say it is progress to recognize your weakness here and treat it with laughter. You are right that no matter where her head is, that purchasing a card (if she did) was hard for her.
Anyway, if you need help building your arsenal of self-directed arrows, here's one to consider adding. Maybe, she'll write: "I used that 2 for 1 coupon for Hallmark. Boy, it was especially tough to find a card that worked for both of you, but I didn't want to play favorites."
In all seriousness, I'd put my money on some note that tries to get her off the hook, to relieve her guilt in some way...
Something like, "Dear H, you are a wonderful man and a great father. I am so sorry for putting you through this, I just need to do this for me right now."
If so, I'd suggest you validate for both your sakes, and validate both sides. Wow, thanks for the card, it means alot to me that you recognize and acknowledge my hurt. And, I know that you are a good woman and you don't want to cause me pain. It must hurt you too because you are a caring person. I understand that you feel it is truly what you need to do right now. It must be so hard to be in that position and I know it takes a lot of courage for you to find your way through it.
Now look, I know it would be hard to say such stuff. But, first, it's true, or you wouldn't want her back. Second, the overwhelming guilt she feels is a huge barrier to her being able to have an R with you. Third, though you may not see it, she really is brave (if misguided) and taking steps to become happy, as painful as the process may be. So, acknowledging that it is important for her to own her own happiness is not a bad thing. It doesn't mean that you think she is taking the right path to do it. But, the compassionate you knows that we will all have misteps. The greater our pain, the easier it is to stumble.