Lisa, welcome! I'm glad you found us.
I highly doubt what's going on with your daughter has much to do with parenting skills. In fact, you sound like you're on top of things in terms of getting her evaluated. It's great that you have an appointment with a developmental pediatrician. That's the first step we often recommend when a parent is struggling with a child your daughter's age.
Did you ever get a report from the SD following testing? Just wondering if it would lend a clue about what might be going on.
Sorry for the questions, but they might help us point you in the right direction for further help:
1) Any developmental or speech delays?
2) Any sensory issues (sensitivity to loud noises, clothing tags, food textures, for example)?
3) Any mental health issues or substance abuse in the family tree?
4) Any quirky behaviors or strange obsessions?
5) You say she is aggressive toward peers, but is she able to maintain any normal peer friendships?
6) How does she sleep?
7) Does she seem extraordinarily anxious about anything?
Again, welcome.