how does she both reject the sterotype and use them to her advantage?

You are referring to the stereotype of a woman as the weaker sex and she rejects it when she asks the "spirits that tend on moral thoughts" to "unsex me here."  She asks to be filled with cruelty from top to bottom which is more stereotypical of a man.  However, when she greets Duncan and welcomes him to her castle, she falls back into the good hostess role and acts perfectly feminine.  Finally, even though Macbeth has talked himself out of the murder, she "reconvinces" him by using both her feminine wiles and her determination through shame to get him to again agree to murder Duncan.