I think that you're not being unreasonable to feel the way you do, but if your DD would like to try it, it would be worth considering very carefully. It could really boost her self-esteem.
I would tell the host that you're unsure if she'll settle, and that you're happy to collect her at any time, night or day, even 1 or 2 am.
DD1 is 12 and has SN, so she functions in some ways much more like a 5-6 year old, particularly emotionally. She was invited to a sleep over with a new friend and my stomach flipped. She was excited, but also pale with nerves.
We talked it over, and decided that as she would have bear with her, and I could go and get her at any time, night or day, if she wanted to come home, for any reason, she would try it. I told the Dad that I had said that to DD1, and that she could call me, or he could call me, even at 1am or 3am, and I would drive out to collect her. She had a brilliant time! She did it, and she was proud of herself.
Your DD1 might get tired and want her Mum. She might wake up and want her Mum. Or she might have a good time with her friends and come back home to tell her Mum.