If my daughter thought she could swear, she'd get in heaps of trouble!
Swearing AT someone is also way different to just swearing... and though I'd be happy with neither, if she swore AT someone I'd be horrified.
We're a swearing family too. DP and I say the even the c-word regularly. But just as alcohol is "for adults, not kids," so are many words. She knows it's not on... and she even thinks that "hate" is a "yucky word" (which is what she calls swear words) because I told her it's not a nice word to use... so she'll rarely use that too.
She can swear when she's older - once she's an adult herself. If I ever catch her swearing at someone though, even if she's an adult, I'll have to strongly resist the urge to slap the filth right out of her mouth.