There's only so much you're going to be able to do. Anxiety can be like alcoholism...don't be afraid to ask for help. She has to be willing to accept your help.
What she needs to hear is that many people go through numerous anti-anxiety or anti-depression medications before finding the right one for them. I tried 2 different ones that made me feel terrible before I got on Cymbalta, which has no side effects at all for me. I would encourage her to talk to her doctor or psychiatrist and try something else. Preface it with how you just want to see her happy and healthy, etc.
Anxiety is a brutal thing that can make us want to crawl into a hole and escape everyone. It's not easy to talk about, even more difficult to treat. Not knowing your lifestyle, do you exercise regularly, meditate, and have healthy eating habits? Obviously diet and exercise can greatly contribute to the alleviation of anxiety and if you're not healthy, I'd say for you to change your lifestyle. Then invite her to join you at the gym. Perhaps there's a way to nudge her in the right direction by making changes yourself?