By breaking Molly. No, I'm not making that up.
It's a fucking pain in the ass but if you're curious:
-You need Val as a slave. She has to be a Bimbo.
-Sarah must be in her Doll form (in your room).
-Jane must be your slave and in her Slut form (normal or latex doesn't matter).
There might have been a fourth slave criteria that I don't remember about. If so, it's possibly Julia as a Slut or Ashley in her Party form. Again, not 100% sure. I haven't done it in many years.
Once you've set all this up, speak to Molly in the item shop and cast Flirt on her in order to go on a date with her.
During the first scene, interrupt her with a compliment because... frankly, why not?
Once you're in her house, she'll realize that you have Jane enslaved. So uh... yeah. I forget if you have to say something specific at that point. You might have to? I haven't done it in years like I said.
Next, tell her that she's not allowed to fix Sarah.
Finally, when Val shows up, Molly will leave and say she'll see you. Tomorrow. At school.
Once done, speak to her at the lake IIRC. She'll ask if you truly enslaved those people. Confirm it and when she asks why you didn't enslave her, too, say you don't want her like that (or something similar).
I recommend you doing a LOT of saves - you know you're on the right track if Molly says that she'll see you tomorrow at school, at least. That I know for a fact.