She didn’t need to be closely associated with coverage of the war, though. If anything that’d be a little too on the nose. If you were a nation with a reputation for carrying out assassinations on foreign soil and wanted to strike against the British political-media establishment, and in particular the BBC, then imo you’d find someone with the right blend of news background plus status and profile - who also happens to be gettable.
Imo, it’s difficult to think of a better fit than the newsreader, Crimewatch presenter and BBC ‘golden girl’, living a relatively regular, security-free life that, geographically, was contained, neatly and routinely, between Fulham, Chiswick, and the BBC.
You’re not expecting this to change the course of the war, revenge is your primary motivation, and in that regard the attack is a success. You don’t claim the attack officially because that would only harden public opinion against you further - but unsettling a media organisation that you despise and leaving the Met stumped are definitely part of a satisfying ripple effect.
Imo as a theory it’s simple, and works as well as any other. The problem is a lack of supporting evidence - though sadly that’s true of all the other theories too.