Oh my...these things are often hard. Have you considered that why it hurts so much, even if as a Buddhist you can let her go, may be that she allowed you to project a fragile and vulnerable part of your self onto her? Many Masters take care of their inner Submissive by projecting it onto another, as many Subs get to know their inner Dom by seeing it in their Master. Love her, whether she is here with you now or in another part of this cyclical existence, and know that as we are all connected a very real part of you went through all that she experienced in her transition. The fragile inner part of ourselves is often unprepared for this kind of trauma, but if you can keep coming back to loving kindness it will see you through. Have compassion for her, for the driver, for yourself. Let yourself feel what you need to. I hope this helps, really I do. My heart goes out to you.