The game is an RPG, the player's choices play a part in shaping the characters. What ehct2332 said about the relationships with Robert and Mike can be true, Lena's relationship with those guys can be a way of working through feelings she may have developed after her traumatic break with Axel (treating Robert like a boy-toy, in the same way she felt toyed with by Axel; seducing a hot guy like Mike into cheating just to get some great sex, in the same way it was done to her), but those things are only really true if the player supports them through their choices, they can just as easily not be if you don't have your Lena pursue them.I just don't feel like this is reflected in the story at all, at least not in all the paths. In my playthrough Lena doesn't seem sexually repressed at all, if anything she seems quite confident in pursuing the desires that's set for her by my choices and she'll even compliment her own masturbation as satisfactory.
In my playthrough Lena only ever fantasized about Holly and the only time her sexual submissivness has come up she had no problem literally burning it away, hell, it even gave her a willpower point to oppose her submissive past. Lena's behaviour forms according to the relationships and opportunities she gains, for example with the Seymour photosoots where letting him havecontrol or not will cost willpower depending on the opinion you allow Lena to have for him.
The only thing that I think can be said to be completely canon would probably be Lena's submissive kink, since that was a part of her relationship with Axel and there's nothing the player can do about it. But like you said, maybe choosing to burn his pictures is a way to symbolize that her traumatic break with Axel has led her to reconsider her desires. Not that they aren't there anymore (they definitely play a part in her appreciation for sex with Ian and how she reacts to Seymour's directing), but that she now doesn't give the desire to satisfy that kink more importance than finding a good partner who won't hurt her like Axel did.