To interfere, or not to interfere?

NOTE: I am not trollin'. I am not making this up to get attention or sympathy. I have this one friend who is the nicest person you'll ever meet, she always chipper (to a fault, not overly chipper), polite, friendly, never swears, never holds a grudge, shes the best kind of person to be friends with. But recently, someone has been taking advantage of her generosity of spirit and has basically been acting like a dick to her. He verbally abuses her, calling her name not even I would use [in that way], and i swear like a sailor! and the worst part of all, is he does this with an attitude of "I know your not going to do anything about it." I hear about it every couple of weeks, and it has reached the point where I am just pissed off... But, bless her soul, she says she can take care of it and she doesnt want to loose this "friendship". I just do not like to see her stepped on like this! This guy isnt even that fit, hes not jock or anything, and Im 6'3" and whereas Im am not a jock either, i like to stay somewhat fit and I can be pretty imposing if I want. But my question is, should I go against her wishes and intervene and tell this guy to back off, or should I listen to her, dont interfere, and hope that he doesnt do anything stupid i.e., anything to really send me over the edge? I mean, im not gonna pick a fight with him (unless he does something to really piss me off when i try to reason with him, and even then, it wouldnt be this big fist fight), im not gonna make a big scene about it. what do i do? to interfere or not to interfere? That is the question...