1) She had at least FOUR doubles in the film.
2) From a brief look on DDG, no interview seems to mention any sheet - myth?
3) Scenes like this are *always* shot with pasties or the likes - no actress would shoot a scene like this with more visible to cast and crew than is needed. You honestly think Chloe would? Particularly given her age at the time? Really?
4) Even if it were not just a trick of the light - she was underage when the film was made. And released. The male cast member there, the producers, director, editors (who, FYI, would have checked any frame for things like this for that reason) would all be in pretty deep legal shit - not to mention from her agent, family etc. And of course the site admins here, who have posted these. "Oops".
5) Pareidolia + desperation.
Either its a massive conspiracy taking in all those people and facts or... you're seeing a trick of the light combined with weird desire. Which is most likely of these two things?
./Done