What is the difference between a nightie and nightgown?

I am a crossdresser and I recently told my best friend. In a conversation with her, I said to her that I wanted to buy a nightgown and she replied "No! you will not buy a nightgown, I am going to buy you a nightie." What is the difference

Nighties are a lot shorter. And sexier. Hehe.

nighties are sexy

and night gowns are old lady ish