Ok, it sounds like she may have injured herself either from a fall or being tripped over or possibly one of the other cats biting her on the rearend. If she was bitten the bite may have abcessed and that is the discharge you are seeing, it would also be painful which may cause her to not want to jump. If she is having a bloody discharge from her rectum she may have internal injuries that are causing this. Either way she should be seen by a vet for treatment. She would need to be on antibiotics and possibly anti-inflammatories to help her get better. I would have her seen soon.
Please click the green ACCEPT if I have answered your question so I may get credit for answering, bonuses welcome. Howl at the moon,soar like an eagle, play like a dolphin, inspire your soul.