I've decided there is no predicting a broody.  She may set and not mother, she may abandon after a couple of weeks, she may protect her chicks wonderfully or not....  
I had a first recently, for me, anyway.  I bought a few chicks to slip under a broody and she kicked them out of the nest.  I have maybe a 5x6 pen in my coop so I put them in there with a heat lamp.  A week or so later, another hen went broody, snuggling down right next to the broody pen.  She sat there for a few weeks, then suddenly decided that the chicks in the pen were hers.  She called to them and paced the chicken wire walls of the pen until I finally opened the pen to see what would happen.  Sure enough, she went about "teaching them to eat."  That was over a week ago and she still acts like she is their mother and clucks to them, although I don't think they ever really figured it out -- they sleep together in a huddle and she sleeps somewhere else, having made a nest as if to cover them in.  They go about their chicken business and she follows them.  I think today I saw some sign she is about to give up, though.  Would be nice, I'd like to start getting some more eggs!
The first broody has now accepted another set of chicks I bought.  Why this set and not the first one, I have no idea, she had been broody for at least a month the first time.
Chickens.....