Why is my baby mute around other people?

When Immie is at home with us she is a right little chatter box. She says a variety of words, some very clearly now including -

- hello
- bye bye
- Beans (the name of our cat!)
- Beebies (CBeebies!)
- Gone/Done
- Papa (Papoose, this is what OH says when he wraps her in a towel after bath time)
- pappy (nappy)
- Beh (Book)
- Mama/Dadda
- B (beddies/bedtime)
- Shush (shoe)
- Fsh (Fish)

And so on. So why if we see people out and about, even people she knows does she go mute?? Once upon a time she used to smile at EVERYONE! Not anymore, now you only get treated to smilies if you are very special!! (Or if you have milky buttons to offer!)

Mama x