Every kid is different. You don't say what level but as it's her first meet I'm assuming she's at a lower level. It's all new/fun for her! Is she a kid who gets nervous? Is she a kid who likes to be busy or needs to chill?
Also, how old is she?
6pm is a late check in for anyone but for a younger child, it's worse!!
My daughter is now 13/Level 8 but still likes to chill all day if she has a late check in. Doesn't want to exert too much energy, lol! Even when she was younger, I wouldn't have taken her to any other activity if a late check in. Plus, if check in is 6, you need to get there early and perhaps allow time to get there....plus allow time to get ready before!
As for what to eat and when, everyone, again, does what works for them! My daughter can eat anything, any time, before a meet. But her friend eats nothing! Go figure!
So, if we had a 6pm check in, she'd have lunch at noonish and then a snack around 3 (cheese/fruit/bagel...again, she eats anything, I don't worry). Then, she'd eat something in the car on the way (crackers/fruit/nuts). Again, everyone has what works for them.
I always make sure she has a bag of crackers in her gym bag to eat when at awards.....esp a 6pm check in they will be starving by awards! Sometimes a little bag of dark chocolate (sorry, works for her, don't judge!) that little bit of sugar helps her at 8pm!
Good luck and have fun!