Bit of a tangent here, and I'm playing devils advocate. She's had her citizenship revoked as she's deemed a threat to national security. Okay.
David Ballantyne Smith sold secrets to the Russians via the British Embassy in Berlin. Jailed, citizenship intact. His actions could easily have caused the deaths of British citizens.
Boris Johnson is in the pocket of Russian money, and met with Lebedev Snr without his security detail present, as PM, and it's just "tsssk.....that's Boris!".
Remember she didn't commit any of the atrocities, she was just naïve enough to be a puppet supporting them.
Where is the line drawn?