Thanks Amylou. It really is hard to know how where the line between "that's just her and she's fine" and "it's a problem" lies.
She started with recognisable words other than Dadda/Mamma at 10 months, phrases at 12 months and was talking my ear of constantly at 18 months. And even without words she was always able to communicate very clearly. However, for months I wondered why she had such beautiful manners with me, but would never thank a waiter, and why people kept asking me if she was talking yet. Eventually I had a bit of a "Duh!" moment and realised that she only talked to her family and very close family friends. I figured that was not unusual for an 18 month old and didn't think much more of it.
You can also tell how important something is to her by how quiet she is, the quieter the voice the more deeply she feels. And even at home she will often not answer us if someone else initiates a conversation rather than the other way around, I guess we haven't focused on this much because she talks so much that it's not that prominent. Which is to say she has always had a tendancy to communicate only on her own terms and does find it hard to talk about things she feels deeply.
She's just a bundle of contradictions really.