R.I.
Dear S.,
I have a 14 month old daughter and she does the same. I used to live with my sister when her two daughters were growing up and they did the same. My mum says, I also acted just as possessive when I was a kid.
I think its only because small children are very possessive about their mothers and too young to understand much else. The way my husband and I deal with it, is to hold her close and include her but still sitting close together,so she gets the message without feeling threatened. She is a lot more tolerant of out intimacy now that she was when she was a year old. Hope this helps!!!