Her fire isn't made of metal. With her power she can make it a solid flame. Therefore, I didn't expect it to weight any more then a flame and would be easier to move again in her desired way, especially with her strength and speed. She swung all the way downward with her miss, all the while eyes tracking him, so as soon as she could she started to swing his way to try to hit him before he could completely get away with his attack. She knew there was no way to intercept his attack in time, which is why your guy can still do damage in his post, but she believes she can hit him before he'd be able to both attack and get away. It's not unreasonable (in my opinion) that she could get one attack out before he could attack and retreat completely out of her range again. You have to remember that she's really fast as well.

As for changing the positioning of his attacks hitting her, she is bending her knee up and away but that doesn't mean your guy can't just do the minor adjustments to move in just a bit closer to keep his slash going as planned. Her twisting would change that blow to more of a frontal blow, but she needed to twist a bit to get into a better position where she could attack. She's willing to deal with the consequences if she's able to get her attack in.

Ah, and she might fall onto her butt with this position she's in, as previously mentioned with her being unstable.

EDIT: Although if this only makes sense to me I can edit it