Just search breaking broody hens and lots of info will come up. The way a lot of peole break them depends on the hen herself. Case and point, my friend has a cochin who will hatch ice cubes, the bird will only stop after 21 days no matter what. Then she has another little cochin that can be broke from being broody by just throwing her off the nest three days in a row.
One of the best ways i've seen and it gets the least bad reviews from other flock owners is the wire bottom cage. Basically make or buy a wire bottomed cage, add broody, food and water, and hang up or suspend the cage to keep air flow under the bird. Works for most situations.
As for the will she stop on her own question....yes, just not sure when.
Is it bad for her to be broody....depends on you. If you have no need for a broody then yes, its bad and you can break her. If you dont mind not getting eggs from her, you have plenty of boxes for the others to lay in, and the othr hens aren't picking on her then no not bad at all. Going broody is natural and they are created to do it, we just have to decide as flock owners if it's a problem for us and take appropreate steps from there.
Hope my rambling helped out a bit. Merry christmas