You are their close friend, and your friend is going through a very tough time in their young life, as much of a core experience as a person can have, and they need love and guidance, not abandonment. Modeling that on both sides would be detrimental for life.

Talk to your friend, feel their feelings, and help them in their next steps. Perhaps that's already happening with her family. They've certainly noticed this odd behavior, too. As her friend, perhaps you should meet them, and help support whatever strategy they are following, or if there even is a strategy. They may be overwhelmed, too, and may welcome your assistance.

Or maybe not. Be prepared for that, too.

Be her friend, don't quit on her, and someday, she won't quit on you.