This book I recalled seeing at a nursing home one day and it's been on my mind ever since. As best I can recall, the plot involves a woman going to live at what sounded like a mental/medical institute or center following the death of someone she was related to, either her family or someone she was in love with. While at the center she begins to realize she has a mysterious power and begins to learn how to control it with the help of a male stranger.
As I can recall the cover artwork included the woman sitting or standing in front of a tree while the male character stood in the background. The sky was something of an orange color, like it was at sunset.
I think the title had a variant of the word "witch." "Witching," "Bewitching," "Witchery," something like that.
Judging from the cover I think it was published some time between 1980 and 1999. It definitely wasn't published recently.