Well, the golden rule for business seems to be “personal problems are to be left at home” and clearly that is not the case here.
If she is a good manager that you would like to keep if she didn’t have the personal baggage right now, then suggest that she either quit in good standing and be rehired when the situation resolves or demote to a “less important” position with hours her ex can’t always count on her being there with (and hours that if she had to be a no-show, wouldn’t kill you, as well).
See, with him lurking around…it’s now not only her safety that is in concern…it’s all of your employees (and obviously, her children are involved, too).
One of these days, he could “go postal” and come in on her, or another worker thinking she should be there at that time, and that would not be a good thing.
The scenarios above are what I would do in your shoes…for her safety as well as yours.
ETA: If she continues to be a no-show with no communication, honestly, I’d call the police and request a welfare check because of what’s going on. You don’t know if she just chose to not come in, or was withheld from coming in. SO scary.