I think people have different experiences of funeral homes and viewing the person they lost.Some see them as being at peace and take comfort from that.
What I saw with some one I lost was emptiness a body with no soul,A heavy metal fan,guitarist with green eyes and a cheeky smile,now in a pale blue silk lined box wearing a suit because those wernt my decisions to make .What I saw was not him,because none of it was about him.Like you that picture haunted my nights,I was afraid to sleep,I didn't go to bed but stayed in the chair until sleep dragged me in kicking and screaming then showed me that picture.But there were other pictures,the real pictures,the cheeky smile,the rock t shirts,the guitar,the joiner with a pencil being his ear,the guy who rescued the scruffiest ugliest dog in the world and brought it home,who played with my kids,helped them with their homework,brought me bluebells.told daft jokes. So I collected those pictures and in my mind put each one onto a card.So I had a pack of cards and only one of them was bad.When sleep out the bad card in front of me I threw it out and replaced it with one of the good ones.Over and over again,until eventually I knew the good ones much better,spent much more time with them,knew all the details,but the bad one faded,it wasn't him,it had never been him and so I didn't look at for the length of time I did the others. It was weaker than the others so it faded to blank and one night I threw it down and it didn't come back.Sure I could bring it to mind but it never got there on its own any more.
You could try that as I did purely with pictures in my mind,or if you have a photo of a good memory,of how she was in life.Put it next to the bed and every time the bad picture turns up switch the light on and look at the photo,rather than allow that upsetting image to stay.