I would say it was a jab, just because she knew what caused the first cutoff. It was a comment about your weight. So, IF she wants a good relationship and wanted to extend the proverbial olive branch, what ON EARTH would possess her to send you a card that deals in any way with weight, even if it's a joke? There are SO many generic cards out there, so I just come to the conclusion that she had to have an agenda to choose this specific one.
So at the most, she was trying to bait you and insult you, and at the least, she's an insensitive idiot. You don't need to be around either type of person. Because even if she's an insensitive idiot, you'd still be on your guard around her.
I'd let your dad make the next move. Let him contact you. Be polite but don't mention the GF or the card. If he wants to ever meet in person, then you can make it clear that you will meet him only, and you will leave if he tries to ambush you with GF again.