When I'm singing with her, I use my own vibrato (naturally). I never try to match it because when I sing with her I mostly listen to myself, but only use Ayu as like a back up.
If I'm using one of her instrumental tracks, I usually keep my own vibrato. Only in a couple of cases will I use her vibrato, like in the end of "Mirrorcle World." The back up voice uses the same exact vibrato as in the main voice, so it sounds weird if it's not matched. But even then, I don't move my jaw majorly. I simply use my voice, but that can't be good...
