Original Description:
Rarity address the big elephant in the room making Purple very calm and relaxed.
EXPLANATION TIME!
How Rarity knows it? This is a part that I erase from the comic because it was too long.
Rarity in her shops, saw tons of time stallions and mares wanting to buy clothes of the opposite gender but never bought them because they were afraid. That’s how Rarity know about Purple and knows how to handle the situation.