Strange baby behaviour

Just wondered if anyone could shed any light or give any tips!! So my LO is just over 3months. She smiles for me and daddy however any other family member i.e grandad or uncle or grandma she absolutely screams the house down as soon as they look at her. Yet we were at McDonald's the other day and a woman who works there as a cleaner came right up to her face and said hello and she was all smiles!! So I don't think it's strangers :/ she seems to be ok with my mum and sister but my dad, brother, dads wife, partners mum and dad she just screams for!! And she sees my dad and partners mum most yet she doesn't like these two!! I just don't understand!! Any ideas or anything I can do?