i disagree strongly. for one, i think it's a dumb idea to go off an do an away rotation in a field you're not even applying to. also, you can REALLY improve your chances for matching at a program you may not have matched at otherwise if you do an away there, do well, and get the support of the residents/fellows/attendings you worked under. now, if you're a jerk or a goof off (like the girl in the story), and you can't hide it for a month, then i'd agree and say don't do the away rotation. if you're not sure of your capabilities or feel that you can't perform to a level equal to your academic record (again, see girl in the story) then it's probably not a good idea to do the away rotation. it depends on you as an individual. it also depends on who you meet there, their positions, and how willing they are to support you. this you don't have a lot of control over, but, if you work hard and do well, the worst case scenario is that you don't get any added benefit but at least know a lot more about the hospital, the residents, and the attendings in the field you're interested in and can make more of an educated choice, and the best case scenario is you get a lot of support from the people you worked with and have a much better chance of getting in.
and i'm sorry to say this, but if the person showed up late everyday (which means she didn't care about the rotation at all), she doesn't deserve to be ranked. clear and simple. what kind of resident will that person be when she's on a rotation she's not super interested in? if i was in the shoes of a PD and had some student not showing up on time at least regularly to rotations (1-2 times is excusable) and apparently blowing it off, i wouldn't want her in my program.