Do I have to accept that my daughter's untidy?

My 21 year old daughter is home from Uni for the summer. When she was a child, I would insist on her room being kept reasonably tidy and clean - not pristine or anything, just not a fire or health hazard! When she comes home now she says that it's up to her what she does in her room and that she's an adult. But I can't bear the mess! Am I being unreasonable? I can't help but think that I wouldn't visit her student house that she pays the rent on and trash it like this. I don't want her to feel like a visitor when she comes home, but then I do think that being an adult comes with responsibilities to others. If it matters to me, then shouldn't she respect that? I just don't know. Suggestions please! Thank you in advance.