Boxer, unless there is something wrong, hogging a mane won't stop it from ever growing. It's like cutting a persons hair.
It takes a fair while for a mane to grow to a decent plaiting length after being hogged. I would suggest keeping a neck rug on her to hlep train it to lay down, and avoid the 'mohawk' look. My little arab had his mane hogged September last year. I didn't neck rug him so he had a mohawk until his mane was about 6 inches long! But now it's about ten inches long and laying flat again. It will depend on how fast your horses mane grows, it's always different. You could give her eggs/sunflower seeds/sunflower oil/Canola oil/Apple cider vinegar and garlic in her feed, all will help with the health of a horses coat and mane/tail, but I don't know of anything that will actually make it grow faster. Good luck!