That's a nice little Bandit.
Your sister is lucky girl.
My sister learned to re-build Honda singles and was a pretty good rider (even her ex-husband used to say she was way better than him - true, she had 4 brothers riding bikes and he was a wuss with a Z-1)
Only issues I've seen with the 400 is maintenance, 14,000 red-line needs correct clean oil and filter or big ends can fail (possible on anything if maintenance isn't done though)
Valve adjustment is simple, carbs work well with those K&N's although I can't remember jetting (600 motor uses 117.5 with K&N and 11,500 red-line, so smaller than that?)