Normies that have only recently started following Chris after the merge don't know Barb's history of being weird around Chris. They think she's some innocent old lady who was raped by her son, not a manipulative abusive whore with her own history of being disturbingly close to Chris. It's not tough to make an argument that Barb groomed Chris into developing an oedipus complex in the first place.
Assuming the jury is unfamiliar with Chris, and Heilberg brings up how Barb forced Chris to spoon her, how she was handsy with him in public and all that shit, it would not be hard to make them at least consider the possibility that it was consensual.