Agreed that it'll be something like this, or the other possibility I see is that she'll have been quietly let go for some breach of a 'social media policy' by announcing Steve's suspension / alleged racist remark to her thousands of followers.
I worked in a volunteer organisation some years ago which was also media-facing, and volunteers had to sign a social media agreement. I'd be surprised if Kate didn't have to do the same, and considering other past incidents influenced by her online following (notoriously the 'it'll take the cunt ages' debacle) I could see her not being asked back.
On that, I suspect it's more she's been not asked back, rather than 'sacked', as we'd have heard about it from her by now surely if sacked.