Just curious what people think is a good age for teenagers to stay home alone, overnight?

My brother & SIL's first bub is due now and we'd like to go see them when bub arrives. The issue is that they live 3 hrs away from us. Our 16 yr old DD works part time and is more than likely going to be unable to come with us at such short notice but she suggested that perhaps she stay here at home by herself.
She's very mature for her age, reliable and I know she isn't the type to throw a party or get into mischief. She has 3 friends that she works with who live the next street over from us, so I know that if she was concerned, she could go to one of their homes.

I'm just torn. Part of me knows she could do it and would love the freedom & responsibility and yet the other part of me is worried she may be too young.

Thoughts?