I guess that would make sense if Lena has a really low standing with Ivy but otherwise I don't see it happening. The part where Ivy had Axel at the club was a bit shady but since then she covered for Ian multiple times in regards to Axel finding out he's dating Lena, she was also honest with Lena about this during the molly scene.
Other than that I really think Ivy is Lena's friend and not a backstabbing bitch. Remember how she still feels loyal to Lena since she helped her survive highschool. Unless something drastic happens I don't see this changing just for the sake of it. Hopefully I'm right about this in the end ... we shall see.
Ivy is the equivalent of Jeremy. She's been presented as a "good friend" and is popular among fans. This means cheating situations involving her, if it exists, will be initiated from the player side.
Ian will probably have a choice to go for her. Depending on her relationship score with Lena, she might put up some cursory resistance. Then maybe you can spend a will point to cheat.
I doubt Ivy will be initiating some devious plan, regardless of her relationship points with Lena. I can't really think of any route decisions that depend on relationship score. It's mostly just flavor text.