Is this too much!?!

So I love my mother but she can be so dense sometimes. She lives with use during the week becuase she looks after our 22 month old. I want to tell her I am pregnant but I know if I do she will start telling people. But like it will start with people who she thinks won't matter and then it will spiral from there until everyone knows. I have a history of Miscarriages so I don't want to publicly announce until I get past that 12 week mark. I just feel so crappy lately and tired and turing down wine at dinner....!?? I just feel like it is so hard to pretend that I feel great when all I want to do is go lay down or sit on the floor in front of the toilet. I was thinking of drawing up a simple NDA and getting her to sign it before I tell her, just to get the point across how important it is for her not to tell anyone. What do you think?