Not sure why you are talking in a different person, of "you"...
Anyways... I would just ignore it, I see nothing wrong with her letter, but b/c you have history with her you are seeing something passive aggressive there, which may or may not be true, but why push it. Since it's a reply all, others will pick up on some sarcasm as well. Also, the letter you sent to your dad was fine to send to him, but obviously it got sent to people on the list... and for that it was rude and likely embarrassing. I feel sorry for your dad, there seems to be a lot of pettiness here. Everyone just needs to learn to get along, harder said than done, I know.