Thankfully this sort of thing hasn't happened to me often, I visited an elderly ladies home the other evening, as I have done some cleaning and odd jobs for her, I let myself in and called out to her, and see she was having a seizure in the chair, and her eyes rolled back, couldn't speak, or I presume hear me, I called 999 they took her off to hospital, but she died a day later, It keeps going round in my head and I keep seeing her in this distressed state in my mind. Will this start to fade in time.
Don't think something like this memory ever leaves you but hopefully it will fade with time. I don't want to go into it but have a good reason for saying this. Take care and get some help.
Would it be possible to get a photograph of her? perhaps smiling, (as most photos are) it would be something to look at & think about her looking happy & not as you last found her.
If not, try to visualise her as you knew her alive & well.
There are Buddhist meditation techniques similar to this, one on equanimity comes to mind.