Over reacting?

Sharon
Ok so here's the deal. My SIL and I have a mutual friend. Let's call her A. I introduced them but they've hung out more than A and I have. So A invited me to a fun night at her moms house... Bunch of friends, fire, celebrating the new year. Her moms house is in the next city over and my fiance is very protective. Our car isn't running right now so he asked me not to go because if anything happens he has no way to get to me. Also, I'm 21 weeks pregnant. A extended the invite to my SIL. She's a single parent, but we all live together in my SOs parents house. I expressed to my SIL that I was upset for not being able to go because it's been a long time since I've been able to leave the house and have fun with friends. So instead of my SIL asking our parents to babysit her 2 year old (their grandchild) she decides to ask me. She said she already knew our parents wouldn't do it and she doesn't think our brother will. So knowing that I'm upset about not being able to go anywhere, she asks me to babysit so she can go have fun at "party" that I was also invited to. I'm only accepting because she's got A paying for baby-sitting as a bribe to make me say yes. If my SO wasn't between jobs right now I wouldn't even care about the money. But right now we need it so I said yes. I just feel like it was really disrespectful for her to ask me. She didn't even bother asking one of the other 3 people in the house she just came straight to me. Her words we're "since you can't go would you babysit for me so I can go? " and honestly it made me feel like crap. My SO have been on 2 dates in the past 5 years (since our son was born) because we are always told no when we ask for a babysitter. We never ask anymore because we're so used to being told no that we just expect it. Meanwhile, our parents have babysat for SIL numerous times because she is a single mom and they feel bad for her. I feel disrespected that she didn't even try to ask anyone else knowing that I was upset. Knowing that I wanted to get out of the house too. Not to mention that her 2 year old is still on bottles and wakes up throughout the night and she will only go back to sleep for SIL. If she even sees anyone else then she won't go back to sleep. And on top of that I've had insomnia for almost 2 months now and the time she wants me to babysit is during the time I would normally take a 2-3 hour nap before I'm up all night. So I'm going to be watching her 2 year old, who I pray won't wake up cuz she won't go back to sleep for me, while I'm exhausted and won't be able to sleep, so she can go have fun at a party that I was invited to. Am I wrong to be upset about that?