Interfering family

Is anyone else having to deal with interfering family at all as it's driving me crazy! 
​My partners sister is beginning to cause arguements with me and my partner now and it's really stressing me out... 
Since day 1 she has just constantly tried to take over, first she posted my pregnancy news on Facebook even though we specifically told her not to as we wanted to announce it ourselves (obviously!) and as me and my partner don't use Facebook we weren't even aware until people started congratulating us!!
​Since then she has bombarded us with gifts, pressurised me to do what she wants, even named my baby!!!!! 
​Yesterday I exploded as I just felt I cannot take anymore after she had sent me pictures of clothes that she's going to buy 'her boy/girl' (her words), most of which I don't want my child dressed in. Last week she informed us that she was off to get the baby his/her first local football kit, it does not take a brain surgeon to realise that these are all things that a parent would want to do themselves?! 
​Sometimes I feel so overwhelmed with her controlling behaviour I feel I am going to have a panic attack! ?