Ashley (left) and Mary-Kate Olsen
Ashley Olsen tells PEOPLE exclusively that her sister Mary-Kate's eating disorder was something she'd "been struggling with for quite awhile" before her family stepped in and sent her to a clinic earlier this month.
"She's hanging in there," Ashley,18, said of her twin sister. "She is taking the time she needs for herself. Right now is especially a good time right before school so she can get healthy." The twins plan on attending New York University this fall.
"I think this is an issue the girl down the street can have," Ashley said. "It's an issue a lot of people deal with."
Ashley said her family "really appreciate the support we're getting from our fans and everyone else. The support's been really amazing."
Ashley declined to talk about her contact with her sister. "It's private. I'm here for her whenever she needs me, and, you know, that's how it works."
For more of Ashley's exclusive interview with PEOPLE, get the upcoming issue, on newsstands Friday.