N.W.
There's really not a lot you can do to make it better, you've already gotten sitters that are fun, and you've made the night like a party.
The best thing to do is reassure your daughter that you will be back and she will have fun, then LEAVE. If she starts a tantrum, ignore it and walk out the door.
And make sure the sitter is aware this might happen and that she is comfortable handling the tantrum.
Chances are she's upset for a while...then gets over it quickly when there's pizza and fun.
She's just trying to get you to stay at home so the more you focus on the behavior (even telling her later that it's not nice to tell the sitter to leave) the more she'll do it in hopes it will work. Once she realizes the tantrums won't work, you're still leaving and she can still have fun, they'll stop. It's very common for kids to do this, you're not alone!
The only other tactic that sometimes works is to have the sitter come early while you're still home. Get the kids engaged in a fun activity with the sitter while your daughter secure you're still around. Hopefully she'll be having so much fun that she'll be OK with you leaving.
Hope that helps!