Girl has suppressed memories raped by a live bat by her brother

I read this book.. I think it was sometime in the 90s I thought it was a major writer like Dean Koontz but I cannot find anything that fits that description in his titles. I seem to remember the cover had a picture of an old house with a spiral staircase on the outside and it was nighttime.
I think it was a family house and her brother had mental issues.
Thanks for the help!