It is What it Isn't - Robin Buckallew - Bog

Tricia begins to meet herself everywhere she goes...a mysterious woman with her face, her name, and her quirkiest habit. It begins to appear she also has Tricia's husband. At first Tricia suspects she has inherited her mother's mental illness, but as duplicates begin to pile up, and more people (and dogs) begin to show up in unexpected places, Tricia becomes convinced she is the victim of a coordinated program to deprive her of her sanity. The problem is, there is only one person who knows enough about her to arrange all the strange encounters, and that is the one person Tricia has trusted the most.