I've got a nineteen year old.
I've had two
When she tells me she's doing something exciting I feel pleased and I feel happy.
So do I, and I'm sure so does the OP
I want her to enjoy her life and do interesting things.
Doesn't everyone want that for their children?
But none of those things means that you aren't allowed to still worried about the "what ifs". My two have been all over the place, and both were away for uni. They are now 21 & 24 and I still worry about them. I still do the "don't bring anything back for anyone else", "look up local rules and be respectful", "have you got your GHIC" blah blah, they roll their eyes and say 'yes mother'. I don't tell them if I have concerns, I don't make them feel like they shouldn't go, but I'm always relieved when they are back safely. They have had a ball.
OP hasn't said she's said anything to her daughter, just that she has concerns. I'm sure if she had said the new boyfriend is a 56yr old grandfather (as indeed he might be) she would have had different answers.
OP she will be fine, and if she isn't she will call you for help.