Ok, so your
woman spends a lot longer in the bathroom than you, right? So it takes you that extra 30 minutes getting out to go to dinner cos' you've got to go back after you're halfway to the restaurant because she needs to change what she's got on.
Vanity, right? Concerned about her looks. Well, no. Check the definition of vanity, Webster Part 2 is a good one, go on, click it now, then come back.
Ok, got that? Vanity is a form of conceit, it's a belief in oneself beyond that which is reasonable. What is happening with your woman, spending a long time doing and maybe re-doing her makeup, wanting to change, asking you if she looks good in something - that is almost the exact opposite. It's doubt, fear even. It might take her a while to feel good about herself.
You see, women aren't, in general, vain. When a woman sees a beautiful actress in a film she might think, 'I wish I looked like that'. It takes a man, though, to come out of a movie theatre actually believing he's Clint Eastwood.
Now that's vain.
This node brought to you by the generalising about sex, race and nationality is a Good Thing(tm), by That Was a joke, son. and the letter T.