A hen who is not feeling well is less likely to run away or move much at all - which can often make them easy targets for a rooster looking for someone to mate, so yes.
More importantly than if she will be bred or not, though, is considering whether you want a bird showing signs of illness in with any other birds due to the issue of communicable diseases and the risk of spreading her illness to others - as well as the issue of the stress of being an easy target not only for a rooster's attention, but also less likely to move away from any other birds who decide to take to pecking at her, etc. since stress only compounds illness and can make recovery more difficult.