You will be the best judge. While rough mating is normal for most ducks, if it escalates to the point that injury likely, you have a problem that needs to be addressed. You said they are preventing her from eating, this is not good. If you want to start conservatively, I'd keep her separate for part of the day and make sure she gets her food and water before letting her out with the drakes, however, given the fact that there are two of them and we are just at the beginning of possible breeding season, and since you said they are your first ducks I am assuming that they are young and just hitting maturity, I would NOT expect things to get better, in fact, I'd expect them to get significantly worse as they mature and spring/breeding season picks up. Good luck.