uhh well she wasnt dating zack when he got shot so there fore she isnt a widow and yes she saw a bit of zack in cloud but when she saw the real cloud she loved him even better
*ahem* Actually, she was dating Zack at the time he was killed. Think about it. He left on the mission for Niblehiem. (Aeris tells you this in the game, 5 years after this all happened.) He escaped with is friend, Cloud, and was summarily shot. He never came back (duh) and no one knew what happened to him. That was 5 years before the start of the game. So she was dating him at when he died.

And about that last part, I wouldn't be to sure about that. She never really met the 'real' Cloud. She knew that he wasn't himself, indeed. But she never actually met 'him' until after she died. And by then she was telling him to move on with his life and stop moping about 'letting' her die.