Going by the 3-4pm hour, the issue I think is her delivery which is rather generic. The questions she asked Michael Fallon were the right ones, but the way she delivers those are not in the same league as Kay or any of the regulars and I'd include Sophy Ridge in that.
The Scottish guy who was on Sunrise this morning covering for Stephen Dixon has similar issues, but I find him an easier watch in the background than Kimberley sadly.
But the secondary presenter on sunrise and the morning shift doesn't have to be a particularly good interviewer, unlike the solo presenter in the afternoon shift. I think part of the problem is that the afternoon shift is currently seen as the least important shift to have a strong presenter on more than anything else, the same effect can also be seen on World News Today on the BBC which oftens ends up with sub-par presenters.