Inversion of auxiliary verbs

Which of the following sentences is correct?

A: "Sheila has to decide who is the best candidate for the secretary position."

B: "Sheila has to decide who the best candidate for the secretary position is."

I think sentence A sounds better, but, grammatically speaking, it goes against the rules - at lest, the rules I acknowledge.

It would be great if you could explain why the sentence is correct. And, if I'm not asking too much, could you please mention the source(s) of information, please? (Grammars, ELT books, etc.)

Fell free to correct any mistakes in my message.

Thank you!