New german shepherd puppy - How do I make her calm down?

We just bought an 8 week old german shepherd. She is sweet and gentle with my two small children, but BARKS BARKS BARKS when you leaver her alone for a second, put her in her crate, or when my sister's pit bull is around. (And they live at my house!) Luckily, the pit bull is very calm and does not bark back or even seem to care, but the noise is driving me crazy. And I don't want my dog to end up aggressive or not tolerant of other dogs. And I don't want her to think barking all the time is okay. Any advice? This is the first dog I've ever had.