Hi, I'd like to help you with your question.
It sounds like this could be one of two things.
One, your daughter has very poor self esteem and does not believe you love her, or probably that anyone loves her. If she exhibits this type of behavior with other people in her life, with herself and has trouble socially, then she probably needs to see a counselor for self esteem issues. She can talk to the counselor at school or you can ask her pediatrician for a referral. You can also search on line at http://www.find-a-therapist.com/.
Two, your daughter is using this to control you. Teenagers can be very good (as well as children in general) at understanding what gets to you most. They know us, just like we know them. What will make you the most upset is what they will use to get you to stop behavior they find undesirable. What she gets by telling you that you don't love her is you making sure she knows you love her and stopping your corrections of her grades and other bad behaviors.
If she was really worried about you not loving her, she would most likely try to win your approval by doing her chores and trying to do well with her school work, so I am more inclined to believe this is about manipulation.
What you can do is start by setting down your rules with her. It sounds like you have already done this, but it doesn't hurt to do it again. Let her know what kind of grades you expect (give a little leeway here, such as "B's" instead of "A's" for the next semester then increase it to "A's" and "B's" etc) and if you need to, set up a chart of expected chores to be done at a certain time. Tell her in a firm but neutral tone. Let her know that if she holds up her end of the bargain, you will award her with more freedom. Then decide what kind of freedom you feel she deserves. Then stick to it. Tell her you are not going to waver from this no matter how she feels about it. Believe it or not, kids do want boundaries and no matter how much they fuss, the fact that you care enough to be sure they do what they are supposed to do helps them grow up to be happy adults.
Here is a book that may help you. It is called Yes, Your Teen is Crazy!: Loving Your Kid Without Losing Your Mind by Michael J. Bradley. It is available on Amazon.com or your local library may have it.
I hope this helped you,