From the sounds of her, I wouldn't breed her, but a good foster mother is valuable, and a pet always gets a free pass.
The rooster paying her too much attention with abnormal bone structure can exacerbate things, for sure. If he's the sort that jumps on a hen who's not cooperating, then he's the sort that risks harming a hen. Injuries often occur to hens that are kept with that sort of rooster.
With these deformed-legged chickens, we don't see the severe leg bending/bowing in most, but it's there and making its presence felt by the abnormally placed tendons and muscles. Even a slight misplacement of these structures can make walking painful, though I'd think she's not usually in pain. Their muscles would have compensated by adulthood.
Sometimes it's only one leg. Their feet often curl to the outside or inside depending on which way the scales twist, but she's not a severe enough case for that; generally when the degree of deformity is that bad it happens very noticeably in the same day or week that they hatch. Sounds like (and looks like) in this case it's a one-leg affair.
I only breed males who let a female be if she protests, because if a hen's hurt or doesn't want to mate for any reason, a male pushing the issue can hurt or even kill her accidentally. Your hen's possibly a good example of why this is necessary. I've almost lost some of my best hens before I started culling roosters for being overbearing and refusing to let a hen go if she resisted. But some hens don't protest no matter what, which is another issue. If she keeps mating despite being hurt you may need to separate her, or him.
If you're attached to her, then keep her. I have faulty animals that I keep despite their non-value as breeders. Even if all she's contributing is a smile to your kid's face, I'd consider that 'paying her way'.
As for treating her... Does she rest unmolested throughout the day whenever she needs to? If she is able to rest and heal, then I'd let her be without separating her. As for pine tar, I would use it if a rest didn't fix up her lameness; I'd just coat her legs and feet. It absorbs completely over an hour to a day or so, depending on the animal. If she's spending a lot of time lying down I'd make sure food and water are within easy reach. Sometimes something as little as a broken toe can precipitate a downward slide to anorexia.
Best wishes.