If your wife find a new job, her new employer can apply H1 another three years for her. But application has to be filed before her old H1 expire.
The "transfer" means "transfer quota", her new H1 needn't quota.
As a transfer case, she can start to work for her new employer as soon as she receive the receipt, needn't wait until approve.
If use EAD, then can't change to H1 again.