Does she come in on her own asking for a treat and you say she can't have one? Or does she bring other kids in with her and you feel you can't give her a treat with them watching but not getting one?
I think I get what you mean about her going out to play and there being other kids on the street playing out as well. I assume they live on the street as well, or live nearby and are playing with someone else on the street. Kids who could just as easily go home for their own drink or snack or treat.
They're not her guests or on a playdate.
So in that case, why can't she come back in alone to get a drink or something to eat and go back out to rejoin the others again once she's had it?
You don't have to feed the whole street ice-creams. It's up to you if you let her take an extra one out to share with a particular friend if it's just the two of them playing together, but nobody would expect you to give ice-creams to everyone on the street whether your DD was playing with them or not.
If she's with two friends you can't really let her take an ice-cream for one and not the other, so maybe have a talk to her and tell her that you can't feed everybody so if she's playing with more than one person then only she gets an ice-cream from your house.
But make sure she's not picking and choosing and leaving one person out by the gate while she favours another. And make it clear that she can only share once each day, she's not to be bringing one in for a drink and another for a biscuit and a third for an ice-cream and a fourth for dinner.
Also, even with just water or cheap juice, if you have a constant stream of neighbourhood children coming in wanting drinks and snacks and the use of the toilet every day, when they could just as easily go home because they live over the road, that gets tiring. You still have a load of kids in the house and a lot of washing up to do after they've gone.