Remember this little gal on the right? I was right that she is indeed from the Lovely Kitty toy line and its cousin-lines (Petite Princess, Pretty Pixies, Betty’s Club), but it seems it was used for the locket playsets. I got a carded one recently that supports this:

Here we see another non-articulated mini-Kitty (or mini-Betty in this case), striking a different pose. Makes me wonder if each set came with its own doll, or if they were randomly assigned like Mighty Max.