Hi Louise (beautiful name, by the way..it's a family name in my family - grandmother's and my mom's middle),
Don't beat yourself up like that. You are NOT a bad mommie. We all have things that go on with our littles that, looking back, we wish we had done different. If your chi is a biter, it has to be really hard to get in that mouth to see it. What's important is that when you did see it...you went straight to the vet and set up an appointment to get it fixed. THAT is a GREAT mommie!