I acknowledge that this is possibly very ASB from the start; my brain refuses to let go of it, however, so now it's here.
Let's say Isabel Neville has a surviving daughter in the 1470 flee to Calais, but her husband George dies. Maybe he goes overboard. Maybe a sea monster eats him. He's pretty annoying - maybe they throw him off.
Warwick goes through with Anne's marriage to Edward of Westminister, the Battle of Barnet commences, everything goes the way it did OTL.
Could we see Isabel remarry? Maybe to Richard Grey, Elizabeth Woodville's second son? They're only six years apart, which isn't horrid. And I can see Edward letting Isabel keep her inheritance if she's married to his stepson - I can see Elizabeth Woodville eventually cottoning onto it, given the whole inheritance thing, but maybe I am underestimating her hatred. Maybe to a friend of Edward's, someone he trusts, as a reward? Does she just go to a nunnery?
What about her daughter? (Most likely named Cecily or Anne). Edward was a pretty forgiving guy, OTL - I don't see him letting his brother's daughter go without her inheritance from her father (or at least a decent chunk of it) or not make an impressive marriage for her.