regardless of the rest of the circumstances, it's a really good idea for any singer to work with a knowledgeable vocal coach. having a vocal coach during the sessions will steer this thing in the right direction. it's not always the engineer's responsibility to "fix" the performance. you wouldn't hand a guitar to a guy on the street and ask him to come record an album on the spot, thinking that u will just fix everything in the mix. singers benefit from instruction, and a vocal coach will not only help her perform better, but also build her confidence. anytime you decide to record a bad performance thinking that you will fix it later is only creating more work for yourself. make this easier, not harder. your recordings will sound world's better when you are spending your time and energy focusing on the sound and not the performance. a good performance makes it listenable, regardless of the sound quality. a bad performance is unlistenable, especially in a good recording. when you don't have the tools or answers, bring in the right person for the job. in this case, a vocal coach. everyone involved will be glad about it, and everyone will grow and get better for it. as an engineer, having an extra set of ears allows you to actually engineer. if you are listening for both the recording and the performance, u will be trying to divide your attention in half and both the sound quality and performance will suffer for it.