Just a reminder that tennis player Dr. Rene Richards in the 1970's was the first transgender athlete to put him/herself out there. Comics made jokes about creating a special category for her - "mixed singles."
Long before Richards, Stella Walsh was a male who lived, and competed, as a female in track and field from the 1930's to the 1950's. I don't know whether she should be classified as "transgender" in as much as she never sought surgery or hormone therapy.
It looks like the IAAF is prepared to argue in the Semenya case that the male and female categories in the Olympics are not going to be based on XX and XY Chromosomes, but rather simply upon a threshold level of testosterone. If that is the case, and Telfer lowers his/her hormone levels to the correct level, he/she should be allowed to compete against XX women, (or anyone else with the female chromosome level.)