I’ve been thinking about you, OP, after reading your initial post. First, as reassurance to you, if your D turns things around, many schools don’t care so much about freshman year grades. So take a breath – the world is not ending. A number of thoughts –
You are not the first parent who has had a older child who was easy to parent in the sense that both you and the child were pretty well aligned in terms of objectives and how to get there. What felt like parenting was essentially being the guard rails on a road you’d both agreed to travel. So this experience is different. It sounds like your D wants to make her own road, and your challenge is to stay connected her while she does it so that you have a loving relationship now and in the future.
I would start by arranging to talk to the teachers in the classes where she is not doing well just to get some input into what is actually going on. (And I would be clear with the teachers that you are concerned and trying to figure out how to support your D, not that you want them to do anything different at this point.) Is she not handing in work? Is she struggling with the material? Cutting class? Any could result in a low grade, but each one may point to a different root cause of the problem. It is not uncommon for a smart kid who has always done well to start to flail when they first encounter more challenge – something they don’t master just by sitting in class. It could be an LD (and the teacher input could help on that), poor organization skills, an inability to ask for help, a lack of confidence when everything doesn’t just fall into place immediately, a lack of discipline, or laziness.
I would then start to work on changing the relationship with your DD. She is a (very) young adult, and she might respond better if she saw you as an ally rather than as someone trying to control/dictate her future. And i’m not saying that you’re doing this (and you haven’t indicated that you are), but to a young person, parental involvement/interest can feel that way, especially if you are envisioning an outcome for her that she hasn’t chosen. Tell her why you are concerned about her grades – not because you worry that she’s “doomed” to a lower tier college but that you worry that she may have regrets when she doesn’t have certain options. If she doesn’t think she’ll care about that, hear her out. If you can really listen to her (in other words, let her tell you about where she would like the road to go), you might be setting the stage for a better relationship going forward. (At the end of the day, I wouldn’t want to sacrifice my relationship with my kid over anything, including my idea of how the HS experience should look.) Who knows what you’ll hear, but she may not want to compete with her brother or is worried that her social life will suffer if she is one of the smart girls or any number of things. Or she may tell you that she’s lost in class and can’t figure out how to get caught up. (That’s a surefire way to spiral downward in classes that build on a foundation, like math and science and FL.)
If she’d like to do better in school, maybe you could both read a book like “That Crumpled Paper was due last week” and let her figure out what strategies might work. I like this book not only for its strategies but for outlining how working smarter can free up more time for what matters. Or you can find her a tutor. But in each case, you should engage her in figuring out what solution might work and then you can help make it happen.
In the end, she is going to be who she wants to be whether you are on her side or not. This part of parenting is so very tough because you CAN see to the horizon when she is living it and cannot. Wishing you the very best with this – it’s really hard…