Well, first of all, thank you for caring enough about your partner that you sought help with how to better-handle her disorder! :) A LOT of the healing process involves being surrounded by people (or just a special someone) who understands and is there through the good times and bad.
I can guarantee you, her silence and sadness has nothing to do with you. My fiance used to constantly ask me "What's wrong?" and I wouldn't have any answers for him, because honestly, half the time, zi didn't even know how to explain my own feelings. It's a very brooding disorder that isn't always outwardly obvious, nor are the symptoms necessarily brought about by certain events. I love my fiance with all my heart, and he is a wonderful, loving man. But he sometimes is still convinced HE'S the problem, when in all reality, he is my rock and my hero.
Keep supporting her, for it is precisely what she needs. And thank you for doing so! :)