I've been following this game for quite a while but I've always wondered. Shouldn't locking the bathroom door require less lewdness to start a masturbation event than having it unlocked? I've always felt that as soon as you start being able to do it in bed, you should be able to already unlock some lewd stuff in the shower or so. And then require that extra lewdness to do it on the open door shower. Also, and that's something I ended up thinking of while playing Soldier's Life, I feel you should have some flavor text eventually in the game about lewdness levels. Something to feel like you're actually progressing through levels.
Like say, certain events that she'll start with something more on the lines of "I would never do that!", then to eventually after gaining some lewdness "I couldn't possibly do that, right...?", to then after gaining more to "It wouldn't be so bad..." and so on, until she finally goes for something like "I can do this", and if she passes a certain threshold of being -too- lewd go for something more like "I can't wait to do xyz!" in a more slutty fashion. So this way lewdness is less just about numbers, but also about narrative and Kate's perception of what's fine and what isn't.
Although, I feel that when it comes to going for a more slutty route, there should be also ways to decrease your lewdness from being a total slut, as well, to just being simply "willing to do" certain things, so that players aren't locked to being an overly sexual girl the moment they achieve that. (aka a point where she's willing to do things, but not super openly), so that Kate can show some hesitance as well when the player prefers it that way. After all even more risk taking people can take a step back, sometimes.
Also as a side note, you should really consider also adding more day to day flavor chat to certain npcs (although I feel you might already be). Like say, the guy in the cafeteria. After the first chat with him, he won't say anything anymore until you start "working" for him. I feel he could've had at least a "Good day, etc." type chat for day to day routine.
I'm certain you might be working on things on order of priority for the game to actually work and go where you want it to, but one way or another I just wanted to give my feedback. I've been enjoying finding out new things every update, keep up the good work!