telling your mil/ bestie

So got a positive last night an although I have no worries with my mum finding out (my ex will tell her when he finds out)  I'm freaking out about telling my mother in law!! She's my best friend aswell and supported me loads (as did her son) when I went through miscarriage in May. I just really don't know how to tell her this time, last time it just came out when I asked if I could go tesco with her.