..
With the variety of molds (and quality) for both Peachy and Lemon Drop, the tale of FF Lemon Drop may have been furthered by the fact that the more common Playset Lemon Drop, the one with factory writing on only two feet, is more of a softer plastic, and stands with somewhat of a lurch forward like the FF ponies do. She's a bit "droopy" and her legs arch in a less supportive way compared to the Lemon Drop that has factory writing underneath all 4 hooves.
I have never seen a FF LD, which is to say. Of course, I am not an expert on variants by any stretch, so someone else may know more. My guess is that, if she doesn't exist, the reason that people have thought she may is because of the reasons I wrote above.. one of the common variations of LD could pass as a FF from a distance.