Demons are funny animals . . . you saw something terrible happen to your friend, and clearly empathized with her pain, so that causes you to be cautious when returning to the scene of her mishap.

It's a fine line between facing them sooner rather than later and giving yourself time to emotionally process what you saw and REASON with yourself that while your friend got hurt at this spot, you can be alert and negotiate the trail safely. You may have to go over that spot with different speeds, different lines, etc., in order for it to feel like it's no different from any other trail you ride. You may always associate it with your friend's accident. Maybe that red light that goes off in your head when your on that section of trail is preventing you from also getting hurt.

Give yourself time if you need it, then face the demons when you're good and ready. To the extent that you have control over your exposure to things that trigger those fears and anxiety, take on what you feel you can handle and leave the rest for when you are ready.

My PTSD symptoms started 5-6 months after my accident. (Months 1-5 I was just happy to be alive and able to wiggle my toes) I got some therapy, then the anxiety and fear came back about 8 months later when I took a new job and had to walk past several construction sites to get to my office. Apparently my triggers are construction sites and sculpture parks. The second time I had symptoms I was better equipped to deal with them.

I may never revisit the scene of my accident. It was in Guatemala, so I'd have to go out of my way. and I don't see a reason to.

Some demons may never completely go away. Chalk it up to some keenly developed self-preservation instincts. Trust your Spidey-sense.