>>713157447 (OP)Because she wore a cowgirl getup and had a Texas sign.
As to why she did that originally? It makes no sense. It's a mountainous village, so farmwork doesn't have prominence, neither is there cattle or chocobos. Her town, occupation and attire has German codings.
Theoretically it could be showing the difference between the early posh, showy and confident young Tifa and the post-trauma Tifa, who's meek, demure, insecure and a wallflower. However I heavily doubt Nomura thought that far.