C..
If she's having a "friends" party - why are there boys and young cousins involved? A "friends" party should be just her friends and geared toward fun for an 8 year old girl.
A friend of my daughter's had her party at Sweet & Sassy - a pink limo picks the girls up and takes them to their salon where they get mani/pedis and their hair done, then they had a fashion show and then ate pizza. THAT is a 'friends' party for an 8 year old girl.
My daughter was big into slumber parties. So, that's what we did - it's not as much work as you'd think. You just throw blankets and pillow on the living room floor order pizza and they watch movies and eat popcorn.
What about an art studio? Lots of times they will do a birthday party. My daughter attended one at a make your own potter place and it was really cool and she got to keep her bowl that she painted. She still eats cereal out of it in the morning.
I still go back to.... what does your DAUGHTER like. The party is for her and her friends. Does SHE like gymnastics? Find what SHE likes and then figure out how to customize it for the people she HAS to invite.