My 9 month old cries violently when I say "No!" in a louder-than-usual and stern voice. This happens when she bites me while nursing. Is it too early to discipline her?

It is never too early. Big big hugs for enduring the pain! When my baby started biting, i unintentionally just automatically screamed as the pain was so sudden! - cannot be helped, it was my natural reaction. He got shocked at first but he continued latching anyway and didn't even cry or get angry. At times when the pain was gradual i would unlatch straightaway, glare at him and tell him not to do that as it's painful. Once he understood what i mean, he sometimes just bite because he thinks it's funny and he doesn't bother if i scream or scold! After 6 of his teeth were fully grown at like about 14 months, i realized that his teeth would naturally just sink into the aerola or nipple so it wasn't his fault anymore - by this time the pain is bearable.