Not only is this a fairly disturbing concept for a weapon, it doesn't look practical at all. A saber of that size cannot be easily swung or even lifted to attack enemy foes, and the amount of Roll's vitals that are exposed means the weapon would be so easily broken it's not even funny.
It almost looks like an excuse to kill Roll while making it look like an accident.
This is pretty awesome (although I agree with the comments that you should keep her head attached somehow). I'd be interested to see more Roll adaptors with different functions, like how Rush formed different armors for Mega Man in MM6.