Can I tell a lawyer she should be volunteering as a lawyer?
Why do you want her to volunteer as a lawyer?
She is really good at what she does and could help a lot of people.
It is wrong to demand people give their services away for free. You can ask them nicely to consider your suggestion.
I just wanted to tell her to do it, this is bullshit.
There is no harm is bringing up your suggestion to her, but accept their answer and don't force the topic. Ask her when she is in a good mood and when the time is appropriate.