I have read this manga a long time ago, because I was reading everything a certain mankaga published at the time. Unfortunately I don't remember who this mangaka was, besides that was a woman, but would easily recognise her drawing style.
Anyway, the manga: it's about this girl, top student of her class, that decides to get away from home during the school's holiday. She even left a letter to her parents saying so...
She ends up at a friend-of-sort doorstep and ask to stay there. I think this "friend" kind of likes her, but I'm not completely sure...
During her stay there I remember she ends up taking interest on the older brother of this friend, and end up sleeping with him.
By the end of the holiday she goes back home...

It's a short manga, don't remember if it was tagged as smut, but this is all I remember of it...

Please help...