I don't have a three year old but she sounds awesome. You sound like a fantastic mum. You haven't let her down at all.

Take the issue back to the CC. They must have some ideas about what they think needs to happen now. A formal speech assessment sounds like a good idea - there is such a wide range of what is normal in children's development. She sounds like she's ahead in other areas and any comprehensive assessment should take into account strengths and weaknesses cause often the strength areas can be used to help the weaker areas develop.

Good luck hun. And stop feeling like you've let her down xx