Seeking advice for Machu Picchu trip — Dad edition

My 19-year old daughter is excited at the prospect of traveling to Peru (including Machu Picchu) with a couple of college friends in June. Other than a chaperoned high school trip to Europe, she has no experience traveling outside the U.S. Her mom and I don't want to squash her dreams, but we also don't have the experience ourselves to help her set expectations.

So...

• With only a few months to plan, what should she be thinking about now?
• What is a realistic budget for her? (They want to save money by staying in hostels, but again, we have no experience traveling that way.)
• What questions should she ask herself and her friends to set some parameters for this trip? (For all I know right now, much of this is a whim.)
• What will help us sleep better at night while she is away?

Any advice for a usually chill but anxious-for-this-kind-of-adventure dad?