She is not 18 hands tall. Several people have measured her with a stick, including Bob Baffert, comparing her to one of his big ones. She was bigger than his horse, but she’s not 18 hands. 17.1 and 17.2 are the measurements I’ve seen most often, including Baffert with a stick at 17.2.
How did she get as tall as she is? Who knows? Some lines do genetically tend to be taller, but there are also cases (I knew one personally, though not TB) of 17 hand and 14.2 FULL siblings. Same nutrition, etc., involved. There are many stories of a breeder in horses in general (not talking about TBs specifically here, but all horses) who had one either wind up taller or shorter than that breeder wished. It does happen. We wish we could “preprogram” everything and design a foal, but we can’t.
There are documented cases rarely of 18 hand TBs (although she is not 18 hands herself). They certainly are not “planned,” as the extra size slows them down as race horses and makes them mature later. But it DOES happen sometimes in TBs. Even if she were 18 hands, she would not be the only TB ever to hit that.
She was not an embryo transfer foal.