Well the poor girl is going through one of the hardest stages of life. I would be depressed too.
Do you really think happy pills as a teen is not a drug problem? Just so you know how kids feel anymore, there is no point in trying to get illegal drugs when you can get **** like Zoloft from your doctor for describing the symptoms of puberty and PMS. And whats worse, the Doctor will give them to you. They see you for what, 15min? How can that be enough time to determine the problem?
So what do you do? Regulate her diet, talk to her, tell her she is pretty, buy her stuff that makes her cool, remind her that you love her 5 times a day.... What made you sad at 17? Well it's messing with her too. Of course she is lonely, she is 17, it is like a requirement. And of course she hates the way she looks, not to long ago she was a "princess" now she has the beginning of a woman's body and that takes some getting used to. And high school is the worst place to be. The teachers are not aloud to regulate the students anymore when they step out of line. As a result you have all the cruelty of high schoolers without any regulation. And we are all told that we should not let words hurt us, but they do. We are told that they are only words and that we need to be stronger, yet when people say things in a mean way that mirror your insecurities it is hard to believe anything good about yourself.
Have her research Cyber School. It maybe the change she needs to get through this. And tell her she is not alone. The school thought I needed drugs when I was there too. I refused them and found alternate ways of getting my diploma. It was hard, but a lot better then letting them tell me I was crazy because I did not fit in. She will find her place, and it will be cool to her, fun to her, and good enough for her. That is all anyone can ask for:)