
I think Kate doesn't know how to let go and fall apart. I think she has a very big, very strong wall built around and probably thinks if she lets down she will, indeed, lose control. Too much is riding on her back now, she's at it solo. She probably feels she HAS to stay strong.
I know of what you speak, I am much this way. It isn't so much about what others think though--it is about what we think of ourselves. it is perfection and control among other things. First time I saw Kate on TV was the Disney episode. I totally saw myself in that ice cream deal.

of course, I then learned that people thought she was the devil incarnate over that clip and really felt badly. If it was about what others thought about her, she'd have edited things like that out.
I seen her do some silly thinks, the wig thing, the pudding etc. She isn't totally unable to have fun. Heck, I remember her having fun with Emeril and people were up in arms about that.

I know Kate could be "mean" and short and rude (esp. with Jon) and I hated watching that but Jon was no picnic either so I hated watching that too.