How mean is this/ should I do it?

Background: My sister-in-law has caused problems with my family since day 1. She is a total nightmare. I have always kept my mouth shut and bit my tounge in respect to my brother. Back during Easter, I sent a gift to their children and did not receive word (or even an email?) that they received the gift. I sent a quick email asking if they got it (maybe it got lost in the mail?) She then proceeded to rip me apart and say that it is very old fashioned to send thank you cards, no one does that anymore. I would have been happy with a text saying "got 'em". She said "I'm a mom, I'm too busy to send you something." (what a bitch)

ANYWAYS, for Christmas I want to send her a gift along with gifts for the kids. I want to send her thank you notes, since she obviously doesnt have them. (haha). How terribly mean is it?

My goal is to make her pissed off, but remember this is the first time i'd ever do something like this. normally i'd just keep my mouth shut. Im tired of keeping my mouth shut.