If her issue is really, truly not knowing the other girls that well -- and not her wanting to have you there overnight because she would feel scared -- then I would talk to the troop leader and ask her if she can keep an eye on your daughter and be sure she's kept busy and included. If you know the parents of any of the other girls, you could ask one mom to have her daughter kind of take your girl under her wing -- without the girls knowing it came from you, of course.
You are lucky the troop leader is offering the "leave and sleep at home and come back" option and that is one I would probably take in this case, if you can find someone to do it. If another girl is doing it, maybe that family could pick up your daughter.
If you think there's any inkling of your daughter's real issue being that she isn't used to sleeping away from you (family camping is different from sleepng out in the woods without mom or dad!) -- then consider going or having her bow out. I"m a GS leader and know how tough it is on the entire troop if one girl starts having issues late at night and you end up calling the parents for a late-night pickup. Tears and fears in one girl can spread like a virus to others.
In some camping places it isn't even possible for parents to do a nighttime pickup if a girl is upset -- We've camped in places that, while not in the wilderness, were down tiny country roads and it was just not possible for some parent who'd never been there to navigate it at 11 p.m. and find the camp safely to pick up a distressed girl.
Sit down and have a good talk with your daughter and try to find out if the real issue is sleeping away from you (She's been on sleepovers, but not in the woods without you or dad there); or whether it's the idea of sleeping outdoors (family camping is one thing, but maybe she's heard about bugs or animals or night noises from other girls and is worried?). You might be able to talk to her and allay any fears. If she insists the only issue is not knowing the other girls that well, assure her that there will be lots of activities to do that will help her get to know them (there will, won't there? A GS camping trip should have plenty to do so that girls don't get bored).
Don't push too hard if she is really reluctant. But do consider finding some way for her to go home overnight and still do the daytime activities.