I think "nonconcentual" is not a term I would use. I think she resisted and was not into it, but gave in to his demands and went with it to try to keep him from getting more angry.
It's a different woman and a different event, but compare this woman's report on Gary in 2010 (posted earlier - transcribed from abc video):
It's a very disturbing and forced sexual assault, with fluctuating levels of protest during the incident, such as when he wanted anal sex.
I contrast it with that incident to convey that I think Robyn went with it to appease Gary's demands, but that she was not into it.
Ultimately, Gary may have been fearful she would be reporting him to the police, so killed her after raping her on that last day she was seen alive. MOO.