OP,
Mary Cain is not on a scale of bad to good with regard to her interviewing. This is not something that needs to be improved upon or likely (in your eyes) ever will. From what I can see, Mary Cain is enjoying life, enjoying competing, is perhaps a LITTLE bit happier and a LITTLE bit more excitable and a LITTLE bit more eccentric than most. Would be cool if we all were more like that. If you want a robot-like interview like the ones you get from 14-year-old gymnast zombies, then you will forever be disappointed with Mary Cain.
Amazing to me that anyone could find it in them to rip on Mary Cain. I can't think of a better ambassador for girls high school (and beyond) running in the last 30 years than her. Consider me a fan. She can conduct her interviews any way she likes. She's doing a great job in my opinion.