[Z]

I think the reason Sharon left was because she hated Dannii Minogue for whatever reason (young? good looking?) and because she lost one of her girls in the first week by virtue of the curse of going on first; she lost the second one due to media scandal and was left with Alisha who, although she tried her best, was never going to go far in the competition. Sharon was left with no acts by the mid-way point; that was enough to push her over the edge and quit. She was just having a strop.