What can she do?
First, DOCUMENT EVERYTHING!!!
Second, she should explain to her boss that her job is to X, Y, and Z. She did A, B, and C in the past to be nice, but at this point she really doesn't want to do them without compensation. (if she is willing to do them if paid) otherwise you can just drop the "without compensation" part.
Now if the response is tough, if she wants to keep her job she needs to do it, or any sort of negative action against her then things get tricky
First, consultation is free with most attorneys. She should consult one and cover what she should and should not do to protect herself legal.
After that she should take her complaints and a copy of the documentation to HR and explain the situation. If things are on the up and up HR will intervene and the situation will improve, otherwise this will likely get nothing done.
If the problem persists she has a few options...
Accept this is the way this job is, and if she wants to keep it she just has to grin and bear it.
Accept this short term and pursue finding a job with better working conditions.
Attempt to piece together enough solid documentation to give the attorney sufficient evidence a legal case could be made and follow the attorney's guidance.
Sadly in most of these scenarios there are negative consequences.
The boss might just fire her the moment he feels she's a liability or no longer doing whatever he wants.
Her working situation with her boss will likely be negatively impacted by this creating tension that could make working there miserable.
Taking on a new job is probably the "safest" in regards to consequences...
Anything involving an attorney to mitigate will create mounds of stress, paperwork, and could land her on a "Do not hire" list.
I would recommend trying to resolve this with the boss then HR, if that doesn't get her anywhere she needs to decide if she'd rather put up with this, or work someplace else. It's just not worth all the effort and frustration to go through formal complaints, legal threats, etc in my opinion.