In Kevin's good ending she get's knocked up so she's not on anything. She probably only lets Sterling on safe days.
I think this is good evidence. Even though the events of that ending are non-canon, I think the consensus has been that facts revealed in non-canon endings are still true?
Besides, while some women do take birth control just to help regulate their menstrual cycle, most who take it do so specifically to prevent pregnancy, and then only if they
expect to have intercourse in the near future. I suppose Ophelia
could've been using it while having sex with David, (if they were even still having sex?). She only started having sex with Sterling recently, and she probably thinks she's safe as long as Sterling doesn't cum inside her while she's ovulating. That's if she even cares anymore. I think she probably
wants to get pregnant at this point, especially after discussing with Sterling how hot it would be.