Interesting that Katie tweeted that she was now 100% healthy so her recent performances which haven't been 100% stellar, do have some mitigating factors. Very impressive progression so far.
In reality, all tennis players are scarcely 100% fit. Some manage their ailments better than others.
I think some of her injury problems particularly the abdominal pulls are related to the amount of torque she is putting through a growing body. Although athletic she hits it very hard for someone who is not exactly muscle bound. One would hope this would settle over the next 2-3 years and she will become better at listening to her body, knowing when to rest.