I would hope that DF would take DD (3 years old) to the mens room. Worst case scenario, what's she going to see? Men weeing. DF is with her, she is safe.
I would be incredibly uncomfortable if a grown man came into the womens toilets, not because I'm a precious old dear but because it's not appropriate, the space is for gown women and if needed, their children. I would never entertain the idea of taking DS into the mens toilets when he was newly TT'd, why would it be acceptable for a man to come into the womens toilets?