It was accusatory because had Leila Moran any prior knowledge of the attack then, particularly as a British MP, she would have been honour bound to have alerted the authorities. In fact there is very likely also a legal duty to do so.
She effected no such alert so any reasonable person would conclude she had no prior knowledge of the attack. The question was a nasty insinuation. But given it was Richard Madeley interrogating I would just put it down to gross stupidity.