Okay, you asked. This is why I view as childlike. You W IM'd you and you asked how to handle it. Fine. We all need some suggestions from time to time on how to deal with a WAS.
IMO you should have waited at least an hour before you responded. Once again she disturbed you at work and didn't even offer you an apology for doing so. You jumped at the chance to do her a favor when she was clearly unwilling to do the same favor for you LAST NIGHT!
By waiting an hour or so to respond a few things could have happened... (A) she would see you don't jump when she contacts you especially while you are at work (B) you would have read the varied opinions on how to handle this and perhaps done things different and (C) perhaps she would have wondered why you took so long to respond.
It's a Friday night and you are a single man. In the future tell your W if she needs a favor on a night you are not scheduled to have the children, especially a WEEKEND night, you require advance notice as your child free weekends are jammed pack.
I would also tell her that she is not to disturb you at work unless there is a true emergency with the children.
