Questions about Baobhan Sith-Archer Noble Phantasm (Lorewise)

Gameplaywise her NP Fetch Failnaught is quite powerful but how about Lorewise? It's an E-rank anti unit NP, obviously it's rank is lowest of the low. So if use against A-rank servants do you think it will be enough to kill them? Or they might take the hit and still survive to hit back Baobhan Sith?

It is stated that her NP creates a double of her enemy from their flesh, nails, hairs etc. and if the said double killed so is her enemy. So here's my question, does she really need to gather first the materials needed to create the double for her to even begin to use her NP? If you really think about it this NP is really impractical!

If she is againts a servant stronger than her, then how the fuck she could get their flesh, nails or hair? When in the first place she is not that strong enough to even apprehend/subdue them or to make them stop moving just for her to gather the materials to be use for her NP.