Graduation party dilemma - ex step daughters

I am dating a man who was previously married. She had 2 daughters from a previous relationship, plus a son with my boyfriend. They were together for a total of maybe 10 years - about 5 of that married. They have been apart since about 2004. The girls have not been a part of his life at all since the break-up. A few years ago, her oldest daughter graduated from high school. We were invited to (although did not attend) her graduation party. We sent a card with $100 since we could not make it. Last year, the other daughter graduated. We were not invited to the party. Should we have still sent a card with $100 like we did for the oldest ex-step-daughter? I feel since we were not invited, we are not obligated to send a gift. A few months later, his ex texted him before the ex-step-daughter was leaving for college and pointed out "you know, she realizes that you didn't bother to send her a card". I'm sorry she has hurt feelings, but my opinion is if you don't want us at your party, then you don't want or need our money. Who is right??