You obviously care very much about your daughter and want her to succeed in life.  Although your daughter did well in elementary school, she has not been doing well since. This kind of sudden drop in grades sometimes happens when a child gets involved with drugs or intimate relationships. However, you do not mention such "lifestyle" problems with your daughter. Do you know your daughter well enough to rule this out? Sometimes arranging for a consultation with a mental health professional for an academic assessment can help clarify the cause of a student's suddenly poor performance. If you are able to investigate the matter a little further and do manage to rule out social reasons for her low motivation, then you may have to just face the fact that some kids are not academically inclined. While they can handle the earlier grades, high school pushes them past their limits. Do you believe that academic success is the only route to a productive, happy life? If so, you may end up harming your daughter with negative messages like "you'll never amount to anything if you keep up this poor work!" In fact, many people have done poorly at school and have gone on to find themselves and their talents in adulthood, often making a fabulous success of themselves in the process. Teenagers who aren’t motivated to do their schoolwork have often experienced the academic world as unrewarding; it has been difficult for them to succeed and after some years of frustration and failure, they finally give up trying to do what they are clearly not suited for. Successful students are usually highly motivated precisely because they have experienced so much positive feedback from their efforts. If difficulty learning is the culprit behind her lack of motivation, then your daughter needs your compassion and understanding rather than your blame and anger. Now is not the time to destroy what little self-esteem she may have left. Now is the time to build her up. You can actually encourage her to find her unique path. You might tell her,  “there are many different kinds of intelligences and school only taps some of them. We have to find your special gifts and abilities outside of the academic realm. Just do what you can until you finish school and explore other endeavors to see what suits you best.” If possible, give your daughter opportunities to investigate other interests and latent talents. Is she a “people” person? Perhaps she would enjoy volunteer work in the community. Does she have an artistic talent? Perhaps you can arrange for some lessons. Does she shine in the domestic arena? Give her free reign in the kitchen and encourage her interest with books, classes and opportunities to flaunt her skill. Everybody is interested in something. If you do not alienate her, it is more likely she’ll open up to you to share her dreams and passions. Excessive criticism for her academic problems can cause her to withdraw from you, however. Once that happens, her future development is jeopardized. She may turn to unhealthy activities and/or people to boost her self-esteem if she cannot turn to you. Don’t drive her away! Show her you have faith in her by finding many ways to compliment her on a regular basis. Refrain from using angry faces and tones of voice in your conversation with her; be warm, affectionate and positive almost every time you are speaking to her (see the 90-10 Rule for teenagers in Raise Your Kids without Raising Your Voice).
As for her birthday, it should be celebrated as a form of unconditional love. “We love you because you are you and you are ours,” is the message conveyed by unconditional love. Half of all love shown to a child needs to be unconditional love and the other half can be conditional love (conditional love tells a child what the parent approves of and is shown by a smile of pleasure upon seeing a child succeed, words of praise and rewarding actions such as hugs or treats). Failure to celebrate a birthday is akin to telling a child, “we’re not pleased you exist.” Such a message would be highly destructive both to the child and to the parent-child relationship.
    Remember, your parenting power—your power to influence your child throughout her life—is directly related to the strength of your parent-child bond. If you weaken that bond through criticism and rejection (no matter how well-intentioned it is), you may lose all of your parenting power. There is only one way that you can help your daughter succeed: that is by continuing to be her fan club, the one who cheers her on, encourages her and believes in her. Tell her, “Honey, I know you will be able to do anything you set your heart on.” From a parent, such words are a powerful hypnotic suggestion. Similarly, however, warning her that “you’ll never amount to anything…” is also a hypnotic suggestion going this time, in the wrong direction.
    You may have to read some biographies of great people to convince yourself that academic accomplishment is only one of many routes to success in life. However, the exercise may fortify you to be able to genuinely support your daughter on her journey.

May be the birthday present your daughter should be given is a two week stay at a wilderness boot camp.  May wilderness survival may help to motivate and modifiy expectations.