This is finally getting some attention beyond the swimming world. The NCAA set the rules and it said 1 year of testosterone reducing therapy and you are good to go. So when he was competing as a male, through age 20, he was a really good Ivy league swimmer and qualified for NCAAs in the mile (means you are generally in the top 40 in the country). He becomes a she and comes back with a year or two of eligibility. Last November in an invite meet, she swims the #1 times in two events and the #3 time in a third. The times she swims in 1 event would have won the NCAAs last year. She isn't that far off from Ledecky's NCAA records. When she swam in that meet, the whole crowd sat on their hands when she finished and applauded wildly for the second place finisher who was literally 30 seconds behind in one event and 2 laps behind in another.
Her advantages gained through puberty as a male aren't anywhere close to being overcome by lowering her testosterone a little bit. It's not clear what her current testosterone level is, but I saw one report that it is still several times higher than the average female. In swimming, having thinner hips, wider shoulders, longer arms, taller, bigger hands and feet are all physical advantages for a male. Then there is the, on average, 30% advantage in strength of males over females that does not completely go away with testosterone reducing drugs. Most research has demonstrated only a 5% reduction in strength. This literally has the ability to end women's sports as we know it. And if she breaks Ledecky's records all hell will break lose.