I feel your pain (see my sister post!) As the wollies said, just don't send the invites. Maybe tell your sis she's the one that's going to look daft when her friends aren't actually invited.
I feel blessed that my sis actually asked after this thread!!!
lets go fly a kite
Just tell her to cop on and if she doesn't remind her she's the one that will look ridiculous when these people aren't invited, or tell her she can cover the cost herself.
Tell her she can have them if she pays for them and then see how many people she wants there.
Agree with Italy!