I said this in another thread but I for one also have a difficult time envisioning the woman in FC being the same one as in X1. It's easy to jump onto the '40 years have passed' argument but ultimately what we got in FC was a character arc that veers to much in the opposite direction to what is ultimately suppose to become of her. I cannot believe for a second that the character in FC with the emotional links she had with Charles could suddenly end up as the character in X1, I don't care how persuasive Magneto is or will be, for more than 20 years Charles had her back and treated her like a sister, and that counts for something in my book, if anything it gives her the ability to look at both ideologies objectively. You see it all through the film that there is great admiration and affection between them, the only way that relationship deteriorates to the point of her becoming who she does in X1 is if Charles is the reason for it. Something terrible must happen to break that bond and it has to be at the hands of Prof X, anything less and the character arc will never feel correct. At the moment the relationship is barely even strained, they depart on good terms, it needs to be severed irrecoverably.