Bear with me while I think aloud.
I think to when I was my oldest stepdaughter's age--just three months older than she is now--and a Morality class at school defined objective vs. subjective. It's the kind of distinction that most people instinctively know is out there, but popular social leanings squelch that instinct before most people can articulate it.
The American Heritage Dictionary of the English Language:
objective, adj., ... 2. Having actual existence or reality. 3.a. Uninfluenced by emotion, surmise, or personal prejudice. b. Based on observable phenomena.
subjective, adj., ... 2. b. Particular to a given individual; personal.
Simply, "objective" is the statement of the moral law (what does God say about doing this in general?).
"Subjective" is the law applied in a certain situation (is this wrong for me under my particular cicumstances?). In America our legislatures make objective laws, and the courts judge individual cases subjectively.
My stepkids have been educated in secular schools. All of their everyday authorities tell them not to "judge." My husband and I see them only on weekends or longer visits.
My older stepdaughter is at the age where sexuality is an everyday challenge--her own sexuality, her friends', her boyfriend's, characters' on TV and in movies, etc. It's very important to show the appropriate level of trust to her. So how do we talk to her correctly, and with clarity, without appearing to unfairly accuse her or her friends?
This is the perfect situation where I think we should talk "objectively." Moral law (objectivity) applies to sexuality just as it applies to science, math and every other pattern of life. Regardless of anybody's situation (subjectivity), it's important to at least know what the moral laws are and what the consequences are for breaking them.
Why not talk about her particilar decision? Even in the rare case when a teenager shares everything about her actions and her circumstances, there's no way for any human to completely know another human's situation. Not even the situation of your own child or parent, stepchild or steparent.
So we're agreed, we have to speak objectively, then let her make her own subjective determinations about when things are right or wrong, and let her make her own judgement as to what is wrong for her. (Yup, she has to "judge" what's right or wrong).
It took me several paragraphs to explain that. Men are so different! A few weeks ago my husband said to her, "I know you have a boyfriend now. You know what's right. You make your own decisions, and I hope you'll make the right ones." How simple he makes it sound!