An obvious answer might be because she is embarrassed.

A senior minister might be sacked by the PM because they are seen as a threat in other words they are too good at their job and must go.

This lady was a junior minister and so far down the list that Boris delegated the sacking. Junior ministers aren't really a threat to the PM so when they are sacked it is for the usual reasons e.g. not up to the job.

Perhaps this lady is looking for excuses rather than admitting that.

Now all of the above is speculation but you asked for a reason, she wouldn't be the first or last person who when sacked tried to shift the blame elsewhere.

Edited by Badger11 (23 Jan 2022 1.06pm)

"Disgruntled ex-employee cries wolf", shock, horror.

She was obviously sacked because she was a duplicitous bltch, and would become more of a risk if she progressed up the ranks. That's why she was got rid.
And Hey Presto, some time later, at a time designed to have maximum impact, she goes to the Press with some unsubstantiated allegation, specifically regarding one her protected characteristics.

She is an oxygen thief.

Or maybe it's because she couldn't indulge in "The Booze Culture"

I have dismissed many, many people. I have never given one the chance to make a claim like this

I would suggest the Chief Whip, Mark Spencer, is at least massively incompetent. Where are his written notes? Who was the independent witness? Were there emails beforehand discussing the removal of this lady from her role? Knowing he was dismissing a recently appointed young female Muslim I am sure he recognised that she had protected characteristics and that he needed to take care.