While this discussion of evidence and burdens of proof is interesting, the accuser here may as well have admitted that there was no sexual assault in the very sentence in which she accused him of sexual assault.
There's no such thing as consenting to being sexually assaulted. Sexual assault, like rape, is sexual contact for which there is no consent, and which is done either by force, by threat of force, or under circumstances where it is impossible for the victim to consent (like drugged, unconscious).
She describes no such thing in her essay. It's actually pretty unclear what she's talking about because she gives no detail, but it sounds like he liked rough/dominant sex, and that she didn't like it but let him do it anyway because she was "terrified to piss him off." She doesn't say she was afraid because of a physical threat, or that he had beaten her on any occasion. In context of everything she's said and written, I would guess her fear was that he would break up with her. Feeling pressured to do something you don't want to do by anything other than a threat of force is not sexual assault.
TLDR summary: regardless of her use of the phrase "sexual assault" she does not actually allege anything constituting sexual assault.