My 4 year old went with my sister and my niece (2.5) on Saturday and they all loved it!!
I think you can't shield your kids from all of the "bad" things out there forever, as hard as we may try. I think it is better for them to learn and see some things when they are with us so we can explain them.
We aren't too picky with what our kids watch or listen to. I think it's much better for them to not be restricted by us, than to go out and go buck wild on their own. Our kids tell us if they see or hear things they should not and will walk away when it's inappropriate. They know what crosses the line. And my kids are 8, 6, and 4.
I think they know because we are teaching them that.
If your 4 year old is over sensitive, there's no problem with that. Just check things out before she sees or hears them, and maybe preview things.
Good luck - because it's going to be hard to shield her from a lot of stuff.