sorry, but does any of this have to do with girls congregating on the streets? i’d like to stick to the topic, so heres my opinion:
i don’t see any reason why girls should not be able to get together outside of their houses. the street is just as much theirs as it is the bochurims. granted, they should not be wild and noisy and have such an animated conversation where they would be quick to draw attention to themselves. and they should at least stay off the actual sidewalk when they know men and boys will be on their way to and from shul. but other than that, like i said, the street is just as much theirs as it is anyone else’s.
as for the boys, if they know there is a specific street where girls are congregating in a non tznius way, maybe speak to someone and try to stop them (for their own good), for we can’t tell the boys to walk down a different street, because the street is just as much theirs as it is the girls.
this goes both ways, and everyone must be considerate of everyone else. girls of boys, and boys of girls. (men and women too!)