they usually sit by themselves at 6mths, or whenever she's phusically ready. don't force her, she'll sit when she's ready. every child develop differently, and if she's healthy she'll sit by herself. if you want to ptob her up, once her back is strong enough, you can sit her in a Bubba (i forgot how it's called, but the mom's here will correct me if I called it wrong, they'll know what i'm talking about) seat, which is safe for her back.