If Lena ignores Axel, it makes sense that she dislikes everyone and anything thats associated with him, like his new girl Cindy.
If Lena still goes for Axel, it makes her jealous and hypocritical to see Cindy potentially replacing her.
And if you really don't want to act her that way, just have Lena act nice toward Cindy.
The scene is entirely consistent no matter the route and entertaining to boot. Its extra spicy if both Lena and Cindy fuck Ian and have to fight over him in secret. Like Lena trashtalks Cindy, just for Cindy to fuck her boyfriend behind her back ^_^