If she has been broody for over two weeks, and she is proven to be good with chicks, then yes. If she isn't currently broody, or if she has never experienced caring for chicks before, she may attack them. Not all broody hens make for good mothers.
Usually, yes. For the best results the hen should have been consistently broody for around 3 weeks. Trying to give her chicks much earlier seems to increase chances of rejection. Lots of folks say to graft them to her at night, but I've done it during the day and had just as good results. I let the chicks get a little cool, just at ambient temp, so they're really wanting to snuggle down under momma when I put them in with her. You can slip them underneath her (from behind seems to work better than trying to tuck them under her breast), or you can just drop them on or near her and they'll find their own way underneath.
A little bit of pecking is normal, even with chicks a hen hatches herself. It's kind of an exploratory thing. She shouldn't draw blood or be persistent about pecking a specific chick. The chicks also peck the momma's comb and wattles a lot, the red color is attractive. That's normal.
People do this exact thing all the time. The trick is having the hen go broody when the chicks are available at your local feed store. Must say I really enjoyed having a broody raise chicks with the flock. Made life easy and no integration to deal with later.
It may just be your luck not to have this hen go broody precisely when you need her to. It is possible, though not real common, to have the presence of new baby chicks trigger the broody hormones in your hen.
This happened in my flock this past summer. Su-su, a five-year old GLW who goes broody several times every spring and summer like clock-work
, suddenly went partially broody when my chicks were already six weeks old. She was fiercely protective of them, even though they were fast becoming close to her size, and she "raised" them until they were almost four months old, teaching them and even feeding them.
I have not tried that yet, but want to. We did have a broody momma hatch 5 chicks and a recently broody mom (sat for less than a week) abandoned her egg clutch and adopted 3 of the other hens chicks (not a happy thing the afternoon it happened). She raised them like her own, crazy Mille fleur D'uccle. Good luck!