The pass rate for top-tier SOF is ridiculously low, as Hangman noted, most male applicants don't cut it. The selection process usually results in a few serious injuries; dudes have also died.
In the military, you are pretty much being evaluated all the time; if you stand out, someone will probably notice. If you stand out positively, someone might suggest you consider trying out something more challenging and help you towards that if you are agreeable to it........be careful what you say yes to!!!
Most dudes don't pass the course; and even if you are the "best" applicant going into the selection process, all you need is one mistake and you could be out, so there's also a bit of luck. You might be asked to try again, but usually you only get that one chance.
Theres some pretty tough, smart & fit women in the military (I usually assume they are dykes...............KIDDING!!), and I'm sure one day one will pass the course (after hundreds of others have challenged & failed). Whether the wives' of the rest of the team-members will be accepting of her is another hurdle to cross.