A month ago I totally would have had the most perfect answer to this question, but now I do not know. Thing thing is that the more you study history, the less you know for sure. I think physics is like that too. Like, you learn the laws of Apples Falling on Heads and whatnot, but as you get higher and higher up in the study of physics, you learn that nothing you learned before is ACTUALLY true and we don’t understand why gravity exists and certain particles know when they are being looked at and you CAN divide by zero. That’s what history is like.
In elementary school you learn that the French Revolution happened because the estates were angry and whatnot, but then in grad school you learn that historians don’t know what event caused the Revolution to actually happen. So there are SO MANY THINGS I COULD ANSWER THIS QUESTION WITH. I think I will be cliche and do WHO KILLED EDWARD II, and such related issues. (I would like to make a Laura Palmer joke right now, but alas; I have not seen Twin Peaks.)
Tbh if I find out via the TARDIS, it’ll probably turn out that Isabella was actually from the 51st century and something about cybermen, so perhaps that mystery is best left as it is~