It can be and it's the only reason Jill is friends with Bella in this case. Because Bella agrees with Jill and regrets what she did. As she'd have firsthand knowledge of the repercussions of such a relationship.
Jill's ONLY against said relationship after it happened and turned out terrible for her sister. She wasn't born against it. But Jill is also an understanding person and Bella being a family friend knew she didn't do this Maliciously she would have a deep seated regret which explains her new ice queen persona to push students away and not draw unwanted attention from students given her... Appealing shape.
edit: It also explains the conversation in Bella's bed between Jill and Bella where Jill storms out to sleep with MC after MC and Bella flirt on the couch. Bella "That's my favorite song" Smile. MC "I know." Jill "It's not happening again is it?" Bella "No."
but I don't understand exactly how Lana would have died in a way related to this theoretical relationship
a suicide? if it was because of the moral condemnation of her family then Jill could hardly have "forgiven" her family, if instead it was because of the way Bella kept or ended this relationship, in the same way Jill could hardly have ever become best friends with the woman who led her sister to unhappiness and then to death
we are constantly reading Bella's thoughts, and for someone who is responsible for the death of a girl (and her best friend's sister), it seems to me that the only guilt she feels is towards her husband.
apart from the fact that they might have known each other I see very little to support this theory.
Also what twist is repeated? 2 times? with this being the third?
Maya + Josy
Chad + Troy
Lana + Bella
when you don't know who the other one is and why no one talks about it, it's always a homosexual relationship