You can choose to stay prude and broke but canonically she is still a slut just like any other girls in the game beside Holly.
Please, tell us in detail how a girl who hasn't gotten laid even once for months after the breakup with her cheating boyfriend is "canonically a slut" in your imagination. Because so far you've failed to provide even a single argument for this theory of yours.
You note it yourself -- canonically she is "prude and broke" at the start of the game and she can
stay this way. It's your own choices which can potentially push her into different mindset.
But the statement Lena can stay decent base on your choices is simple not true. She clearly show a lewd side when you play the naughty route.
No, she shows a lewd side
if you have her act lewd. She does not if you don't. Her mindset is modified according to your choices, It's simple as that.
To provide a simple example: you can have Lena take interest in Mike and flirt with him, or to ignore him. If you ignore him, she describes him as not interesting later in the game. If you flirt with him, she will think he is interesting. Do you believe the variant where she doesn't find him interesting is some sort of a lie because the opposite variant also exist? If so, then why do you pick one of these as canonical where both are equally possible? (and left up to the player)