K.T.
Oh my goodness... That is just like my daughter who is also 10 months old... She will not go to my mother-in-law AT ALL!! She also won't go to on of my brother's either and it seems that she is very specific that it is directed toward them and it is very obvious she does not like to be around them... With my mother in law, I first thought that it was because we didn't see her often enough, but she will go to everyone else who lives at their house, just not her... She went to her in the beginning when she was first born, but I noticed the change in my daughter was when my mother-in-law got a new hairdo... It seemed to scare her... I'm not particularly close with my mother in law, but I feel really bad when my daughter screams almost hysterically whenever she is around her... I think in the case with my brother, he is a little closed off emotionally and I think my daughter can sense that... I think that my daughter "senses" when a person is receptive and loving and is more drawn to that, because she will go to people that she meets for the first time, but will not go to my brother or mother in law EVER!!! I don't know if this will help, but these are just my own personal observations I have made with my own daughter....
Hope this helps...