The CBS show is not the end all and be all of this case though, many, many experts were involved in determining that not only had sexual abuse of some kind taken place that night, but had also taken place before.
There is no simple way for that cellulose to get inside her vaginal canal without someone inserting something (fingers, paintbrush etc.). I know some have stated she could have masturbated, but then when would she have handled the brush? I highly doubt she could have broken the brush herself, and why would she have done that?