The ways in which Isabelle's hypothetical Bertrand trauma would vary from her canonical/Nullverse Alec trauma would give Isabelle more initial anxiety about abandonment and attachment, I think. Having been neglected by Bertrand, she would probably be clingier with Cy, and would go out of her way more to please him. This is also a product of how her sexual behavior would change—Isabelle typically shows promiscuous behavior because she's trying to fill the void Alec leaves, but I think in this case she would do it more to get attention and affection.

However, I also think that Isabelle's increased independence due to Bertrand not suppressing her the way Alec did would mean that she moves on from that phase relatively quickly. She would have an easier time standing on her own and would depend on Cy less for stability once she's internalized that he likes her and isn't going to withdraw from her. Isabelle would also be less "baby mode" and soft overall, so the tone of their relationship would probably be different. She'd need less caretaking of a cg/lg sort and more emotional reassurance.