In most people who regularly practice "rough sex" or BDSM, this type of thing is called "Ravishment Play" rather than "rape." That makes a difference between a non-consensual thing (which rape is)and a consensual one.
Ravishment Fantasies are one of the most common fantasies among women. There NOTHING "wrong with it." It's common and NORMAL. Most women probably have Ravishment Fantasies because our society tells us sex is "wrong" and in a Ravishment, one can pretend one is not making the choice to have sex, although one is.
MANY women have had rape, trauma, abuse in their backgrounds. Some of us have chosen to shed the "victim" idea, worked on ourselves, and dealt with it in a way which allows this type of play with no psychological stress. For some people, it is even therapeutic, as they ARE in control and certainly NOT a victim, as opposed to actual rape, in which one is a victim, at least during the act. Whether to remain a "victim" is up the individual. I worked on my past and choose to NOT be one.
Having a "Safe Word" and
knowing you can stop at any time eases the pain and puts you in control. It can actually be quite freeing. If she has "obvious mental issues about it" then those do need to be worked on, usually in therapy in addition to self introspection.
As long as a sexual act is consensual for both partners, there is not such thing as "wrong." How can something both people agree to and enjoy be "wrong?"