I do not know quite how to express my condolences. Miss Bixby was rather a remarkable young lady, and while I did not know her well, I am deeply saddened by her loss. Yet...I find myself concerned as well. For you. I know you were close friends — and I have never been the sort to judge such an association — and I understand how losing a friend can affect someone. Not from a personal standpoint, but from a point of observation.
I feel it appropriate to say, keep her in your memory, and think of what she would want for you.