The thing is, I'm not sure it's even presentational skills that are the problem. I couldn't care less if she comes across dull or a bit eccentric, but she seems to lack basic knowledge of her field. In the LBC interview she didn't know the details of a key policy on her patch, whilst the recent Sky interview suggests she had equally poor knowledge of a key policy paper in her area. Not having that knowledge is bad enough, but to then try and bluff your way out of both situations makes her look not only clueless but untrustworthy.
It's bad enough that she creates this impression in front of the electorate, but imagine you're a civil servant in the Home Office and she's your minister when you wake up on Friday.