Assuming you are referring to events in Deathly Hallows, the scene you are thinking of explicitly states that Ginny leaves (page 624 of Scholastic paperback):
"Ginny," said Harry, "I'm sorry but we need you to leave too. Just for a bit. Then you can come back in."
Ginny looked simply delighted to leave her sanctuary.
So when Harry, Hermione, and Ron entered the Room, Ginny had already left.
Although, when the Hogwarts students who were hiding from the Carrows in the Room of Requirement began to include girls, a second room was "sprouted" but it was a bathroom (page 578):
"...it [Room of Requirement] even sprouted a pretty good bathroom once girls started turning up-"