The mother didn't want her boy wearing a dress - that's not transphobia!! That's called parenting. She's guiding him in the ways of our current society as any mother would. We don't know that she doesn't allow him to dress secretly at home or whether she's just venting to friends as we women do - not actually thinking anyone expects her to change the world at the same time.
She may or may not be transphobic, but there's plenty of transparanoia here!
