I'm going to second MSD's blu-kote suggestion. The wound looks horrible, but seems to be confined to the surface, and surface infection seems to be the most likely complication..
You will need to inspect her enclosure to determine and eliminate the cause of the wound, for example a leaky water valve or exposure to predators or another rabbit who may have caused injury.
If she was wounded by another animal, chances of infection are likely to be higher. A vet would be helpful in that they could legally provide a rabbit specific antibiotic.
With buns, it's a good idea to give probiotics along with with antibiotics too.