I would have said if she said “I am out and coming home at closing, (I am not sure when that is as I aint a big drinker :/ so maybe midnight) then staying at a friends until the next day is not on.
Just explain if she had planned on staying at a friends then she should have said so you could have told the nipper and put your own mind at rest that she is ok.
She is only 23 like, but she sounds like she does need reminding what her responsibilities are and not taking advantage of you. You clearly dont mind looking after the nipper, but if she said she was supposed to be back at X time, then she should have been. That way she grows your trust and maybe if she was more sensible / responsible in that way, you would do it more? Maybe you could go along them lines.