Just keep him close to you all the time, I find that if you keep pointing at things and explaining things to them then that helps keep them calm & well behaved. Enjoy it

Does she like plushies? Maybe bring those along. Or buy some! Plushies are fun.

A weighted vest or a Pressure Vest is beneficial for large crowds. I wear a pressure vest with a crotch strap when I’m out in public

Go there early or an hour or two before the event ends. Unless there is something specific she is looking forward to seeing or doing there? You can look at the list, schedule before you leave so she knows what to expect.