Just text her and tell her the truth about how you feel. If you don't think she is like on the bandwagon like I described then she shouldn't have a problem talking about your relationship with her. The 7/8th grade thing is just when it happened for me, the time period is irrelevant to a relationship.
People discover things about what type of relationship they want and what makes them happy at totally different periods in there life. This just could be when it's happening for you. Maybe it's not, I'm not sure. If you don't think she's on the bandwagon, then I was wrong in making that assumption. Just how you described her really makes it seem like she is part of that "general crowd" of our generation.
Bottom line is this. If you are in a relationship with someone and are unable to tell them how you really feel or tell them that you are unhappy then it's time to move on. If you can't tell someone who you love that they are making you sad or if you can't tell them how they could make you happy again then they probably aren't someone who you should be with.
You need to be able to communicate with someone if you love them and tell them all the things that make you happy and know how you can make them happy. So you can always be trying your best to be happy together. If you can't communicate this to someone that you are in a relationship with then you should just be with someone else. You need to be unfront with things, as odds are they can't read your mind and won't know if you don't tell them!
Be upfront with her and just tell her you still really care about her and want to be with her(if you still actually do) but you haven't been happy the past few weeks. Don't try to lead into it with something unrelated or sugarcoat it or whatever. If you can't tell her this upfront then it's just time to move on. You need to find someone that understands you so you are able to be happy together with them!
That is my advice.
If you feel like you don't love her anymore, or just don't want to be with her just tell her that. But if she doesn't want to break up with you, and still really cares about you then it would be the right thing to do to tell her why it's not working out for you and why you aren't happy anymore. Maybe she says she can fix that, maybe she can't. Either way you end up happier, and that's what we need to fix here!