Yeah except Fallon Fox was an XY male, taking estroge to resemble an XX female (MTF).
Sarah Frota would be an XX female taking testosterone to resemble an XY male (FTM). Hence why she would be forced to compete with men.
After a certain amount of time/tests, the IOC (and later Athletic commissions) decided those on hormone therapy would then compete with the gender they indentified with/emulated hormonally. It's still a sensitive subject, and one we don't understand 100%. I have less of a problem with FTM's competing with men, than vice versa.
Fallon Fox is bothersome to me however.. she failed to disclose her status as a trans woman to comissions until she was caught. That is 100% wrong. In the interests of fairness, she should've been tested hormonally all the time.