Becoming a stay at home mom...

I'm new to this app and I think it's wonderful for starters. But I need some advice. My husband and I are planning to have a baby. We already have a five year old that's in school. I work full time, I go to school full time, and we are getting ready for baby number two. We would like for me to become stay at home with the kids and my husband support us. I have a pretty important job (head of cosmetics for a dermatologist). I have been there for two years, I brought a cosmetics into this office. When baby comes I want to put my notice in. I'm extremely nervous as it was I that brought cosmetics in. My boss can sometimes be very intimidating and sometimes mean. How should I go about telling her I am transitioning to stay at home mom?