Does anyone else find it strange that for a sexually-liberated mother, Mrs. Flax apparently never talked to her 15 year old daughter about sex (before said daughter loses her virginity that is)?
Not entirely, given how prudish Charlotte is initially. Even if she wanted to, Charlotte may have resisted any attempts.
We must also remember that Rachel's whole primary character flaw is running away from uncomfortable, difficult or painful situations, and giving the Talk to your child certainly counts as 'uncomfortable' and 'difficult'. It's not a huge shock that she would avoid it if she could. Remember also that she is rather self-centred, hypocritical and immature throughout the movie; notice how quickly she starts throwing around slut-shaming in the big blow-out at the end despite hardly having much room for judgement on that score. She is perfectly fine with being sexually-liberated for herself, but clearly doesn't want that for her girls, and while she may make jokes about it, she might assume that giving Charlotte the Talk in a more serious way might "put ideas into her head" (it is still the early '60s, after all). She's clearly not taking motherhood perhaps as seriously as she should be, so she shies away from the difficulties of it.
