Greetings:
It kind of depends. Don't you love cryptic answers?
If she can lift the empty bar on the specific exercise, have her start with the empty bar. Do a few sets to start learning the exercise. If the bar is moving easily and she is catching on to the form start adding weight a little at a time until the bar slows down or the exercise feels heavy.
If she cannot lift the empty bar, and there is nothing wrong or shameful with that, then things get a little more tricky. If you have access to lighter bars (women's bar or technique bars) then try those. If you do not have access to them or she cannot lift those then you have to start with bodyweight. If she cannot perform the exercises with bodyweight, then I would consult a coach because now you have to look into specific assistance exercises that will bring her from pre-novice to novice and that would require more space to write out than the forum allows.