female bunny with a red bottom

Question
What would cause a female Lop bunny to have a red bottom?

Answer
Most likly some runny stool or possibly fur mites.

Keep her bottom clean and dry as you would for a baby.  But don't use any creams or salves because the bunny can ingest them when she is cleaning herself.  

If this continues for more than a couple of days or gets worse, I would suggest a vet visit.