From the World rugby transgender policy.
she must demonstrate to the satisfaction of the Expert Panel (on the balance of probabilities), in accordance with clause 4, that the concentration of testosterone in her serum has been less than 5 nmol/L continuously for a period of at least 12 months
According to the news report, Kelly qualifies to play in female sport under Olympic rules. The IOC rules say that testosterone should be below 10nmol/L. World Rugby say they have made a 'conservative' decision, which seems sensible for a sport like rugby (but it's still dangerous to allow males to play in women's teams).
But they also say this:
she must provide a written and signed declaration, in a form satisfactory to the Chief Medical Officer, that her gender identity is female
We badly need a definition of what a 'female gender identity' actually is.