she has numbness because:
1) she's hanging on for dear life (like someone already said, grip tank with knees, and use the core muscles)
2) she needs to not only bend her elbows, but drop them. if she's on a sportbike, her elbows should be lower than the handlebars.
with time, and experience she'll stop the death grip. I still do it on my cbr 1000rr, esp when I'm on the track. it's got so much torque, I feel like I'm going to fly off when I crack the throttle.
my hands are never numb on my zx6r.
vibration - did you ride the bike? what do you think? I think heavier bar end weights to dampen the 'vibration'.
she'll get used to it, and it won't feel so wierd. put the bike on a rear stand and let her try different positions. so she can get used to it.