Jane Grey was a very intelligent woman but a political innocent, put forward by vested interests in supporting the reformed Church. She had a legitimate claim on the Crown because her cousin's will (Edward VI) had disinherited his sisters. However, the Catholic church was strong and there was a movement behind Mary. The support for Jane melted away and exposed her and her family.
Not quite the same as the Truss situation. For me, this is a new constitutional moment in history. It's not even the same as Eden at the time of Suez.