The way it's worded, I think you are trying to trick us...so I won't jump on the American TC winner and the obvious answer:>)
If the Filly Triple Crown is in play, the first to do it would be Open Mind in 1988 (BC Juvy) and 1989 (Filly Triple Crown).
If it is not in play, it still would be a filly...the Canadian TC winner who defeated the boys in 1991....Dance Smartly, she also won the BC Distaff the same year.
You got me, TJ---Dance Smartly is the subject of this question. (Open Mind's sweep was impressive, but she won the Triple Tiara, not a Triple Crown.)
Lately your questions were in my time, so I've been getting lucky:>) Back in that era, when Open Mind won the Triple Crown, it was known as the Filly Triple Crown. All the races were run at Belmont Park at consecutively increasing distances and the time span was similar to the TC for colts. It was changed to the Triple Tiara after they started changing the track, the dates and messing with the race distances. Changing the original 3 races which comprised the Filly TC. Open Mind won it when the series was The Acorn (1 Mile, 5/27/89), The Mother Goose (1 1/8th, 6/11/89) and the CC American Oaks (1 1/2 miles, 7/3/89). She was one running Jersey Bred who took the Kentucky Oaks before winning the Filly TC:>)
I'm Avalyn Hunter, an author, pedigree researcher and longtime racing fan.