So there is only the one way to gain submission for Sidney, but submission doesn't /have/ to be the only stat that makes her undress for the photo shoots. In-story, she's terrified of losing her "family," being cast out, she feels guilty for what she's been doing to her sleeping "family members."
What if you keyed in the ****SPOILERS**** handjob panty event to give +1/+2 affection. Then you could key 2-3 of the steps to finish her photo shoot to be based off of her AFFECTION. The player pushes too far one shoot, pisses her off, she leaves, her submission goes down, anger goes up... then they give her a gift, her affection goes up, her anger goes down, and they can still make headway with the photo shoot.
Sidney does SEEM like a completely different character than Lauren - like she'd be driven not just by submission but by affection. I assumed that would be the case as I was playing the game, like the Mom's could be based off of Respect, Camille's based off of Libido and submission, and Mandy's based off of Submission and Libido.
Just an idea, of course. It'd make the player have to juggle the different options more during the photo shoot.
I've not finished the game, though I am about 85% of the way through? So i hope none of this sounds dumb!