Hi- She has a reason, you just don't know what it is. There's not always a solid explanation for what can disrupt our brain chemicals.
This is the substance abuse forum. There is an anxiety and depression forum where you might get some support. Click on "forums" at the top left of this page and you'll see it alphabetically.
I feel hopeless without reason a lot, and it frustrates the hell out of me. If therapy alone isn't helping, you need to try the meds. My depression started when I was 15, and here I am now at 23 barely able to function most days, but I've learned in this long period what should not be done, so if you have any questions, feel free to ask me.
On the medication part, I'd try Zoloft first. It's one of the "cleaner" SSRI's and generally side effects are mild, for most people anyway. Oh, and do some research. I've done a lot on meds and the symptoms of this disease and it's helped me at least understand a lot. Good luck!