Probably editing. From what I remember at first there was a close up of him putting a mic close to her chest shortly after she walked into his studio (more than likely a double during the close up), then a lengthy chase scene occurs,and then when he finally catches up to her, he then rips off part of her overalls. Then the next scene you see is her collapsing down a flight of stairs as the older sister is modeling. Older sister then ask what happened, Mariel's character then makes up a lame excuse that she just had to just go pee (wtf)and older sister goes nuts and that's about it.
Maybe when it was filming Mariel might have been told that she was only getting roughed up instead of her character actually being raped. I guess...
I think it could be done if they tricked her into thinking she was being killed in the end of the film, not raped.