Perhaps the saddest aspect of all is that the toddler, if they live, will readily forgive her mother if she sees her again.  Brutes and molesters count on this ready forgiveness to keep on with their atrocities.  There is no excuse for any adult, male or female, to do this type of damage to a child.  While I am not opposed to corporal punishment, there is a huge gulf between what is acceptable and what is not.  Anybody that bruises a child or raises a welt has gone way to far.  For a toddler, a loud no is all you need to get their attention.  As they grow stuff like time outs can take on meaning they understand followed up at a later age by adding loss of privileges is a more effective way of correcting a child.  In no instance is kicking, throwing, shaking, etc. reasonable.  Call for help if you or your spouse are even approaching any of these extremes.