Well, from what we've got so far, there's no overt encouragement prior to Chris telling Bella that he was raping Barb.
When he did tell Bella, there was a lot of encouragement. She told Chris that he was a kind and loving person, and that the relationship was wonderful, and that she sympathised with how much pressure he was under because society didn't understand, and then recommended that he have more fun with Barb before Everfree NW and recommended he do some "romantic dates". She then encouraged him to have sex with Fiona as it would strengthen his relationship with Barb, and got him to send her $500 for a camera so she could take photos of him and Fiona together and make a "romantic slideshow" that he could share with Barb. And that's all from the audio of Bella herself saying these things.
There's reasonable suspicion that she may have encouraged him to pursue this course of action, because of what we know about her. She faked texts from Chris to make it look like he was engaging in BDSM with Barb and described lurid false details about it to discord groups for her own gratification. We know she was separately pretending to be Magi-Chan, who Chris is in a "polyamorous marriage" with and who he considers a "deity" that gives him guidance. We also know she gets off on incest, rape and manipulating people. As other people have pointed out, Chris has often contemplated incest with Barb and had ample opportunity to commit incest prior to this, but never did, and has previously been manipulated into doing things he otherwise would not do, and she was responsible for telling Chris that he needed to tase someone to trigger the merge. Bella refused to release logs that would exonerate her if she hadn't told Chris that he rape Barb.
Chris still raped Barb and that's on him, but I'm giving it 50/50 that she pushed him into it.
