Seriously, stay away from the chick. You situation has bad news written all over it. Even if you did hook up with her, it would probably cause you and your buddy to stop being friends. Also, since he more than likely sent you her pics on purpose, imagine the stuff he would probably send you just to spite you. You would feel twice as sick if your buddy "accidently" sent you a pic of them getting freaky. That shit messes with your head whether you think you can handle it or not. Let it go.... Like E.C. said, try to find another girl because there are plenty out there.