By the way, how intricate is her guitar playing? Is she fingerpicking or is she strumming?

If it's more strummy and not too fingerpicky then she should stop worrying about the sound of the guitar on the first recording - just get a good vocal sound.

Then do a second recording of just guitar (with her first recording of vocals and quiet guitar in her headphones as a guide).

(The reason I asked about her guitar playing is that it's very difficult to cleanly overdub a second guitar part of intricate fingerpicking - you tend to play it differently each time. Whereas it's very easy to overdub a guitar part of strumming)