I would love it if Calia was lying. That the reason she’s reserved telling ANYONE that she had more than one child or her daughter is actually a son was to avoid this very outcome. A son means a scion of House Menethil a daughter would mean little in the game of monarchs. She above all knows that a woman’s claim to the crown is little of consequence to a society ruled by men.
Either her daughter transitioned or Calia lied. I would rather a political spin one which the Scarlet Crusade and by extension the Arathi can use against her. It would also be more brutal if she admitted that she indeed lied and that her daughter is her son. Her son is the Prince of Lordaeron.