I don't know for sure.
Fur like that is common if a rabbit has a runny nose, drooling mouth, or drippy eye. Any of those can indicate sickness, but I don't know details. If the rabbit has any of those, it can also have gunky fur on the paws, from wiping its nose/mouth/eyes.
For where the fur is in the picture, I don't think it's the eye or the nose, and I can't tell for sure about the mouth.
Given the pink spot, she might have a minor injury, maybe something like a bug bite or bee sting. If she's been rubbing at it, that could explain what's going on with the fur.
You say it first showed up a few days ago. Do you think it has been getting better or worse? If it's getting better, you might just keep an eye on it. If it's getting worse, she might need to see a vet. (Nursing a litter, and maybe pregnant again, could complicate any kind of treatment.)
I would probably give her a thorough going-over to see if there are any other symptoms and watch how she acts. If you don't find anything else wrong, and if it does not seem to be getting worse, I would just keep watching for now.
(I didn't respond sooner because I was hoping someone else would know enough to be more helpful.)