I wanna tell my boss about my pregnancy tomorrow but idk how to do it. . I've only worked there for…

I wanna tell my boss about my pregnancy tomorrow but idk how to do it. . I've only worked there for 2 and a half months and I'm pretty sure she'll be happy but I'm still super nervous about it. I know she can't fire me because of it but I just don't know how to tell her I don't work at some big company it's just a small family owned business. Help please