Considering this hen is a first-timer, I'm just a little nervous about her. Maybe I am needlessly worrying, but I've heard stories of broody hens killing their chicks when they hatch. I'd like to set about a dozen eggs to hatch, but if there's a chance she may kill them all, then I'd prefer not to risk it with too many chicks right off the bat. That's why I was going to put half the eggs in the incubator, and then add the extra chicks to her the night after I've verified that she's not going to murder her chicks.
Now I am not sure which way is riskier. Hmm.
I can not find fault with your logic. Decisions, decisions.
I can tell you that of 11 hens that brooded for the first time this year, only two were not good broodies/parents. The odds are good that your hen will do just fine. The two hens, of mine, that failed as broody hens did not kill their chicks, but were poor at brooding eggs.