I don't think that riddle has a solution?
I did all I could solving, the only safe way to do the first move is to take the bunny to the other side. But if you do that you can't bring anything else to the other side, so I guess you were meant to not solve the riddle after all.
b=bunny c=cat f=flowers
losing conditions: CB & BF
| witch's side | other side |
| B C F | |
| C F | B |