Hi Johnny, In this case "bro" is slang, like saying "buddy" or friend. It can be used to refer to any man, but generally calling a woman "sis" is used only if she is actually your sister. The greeting between girls can be different depending on their age. I'm thirty and might address another woman as a chick, or in a group, ladies. My teenage students with refer to their friends as "chickas", or "bay".

If a woman greets you with, "Hi Bro!" then you can definitely reciprocate with, "Hi Sis!" It would be funny, in a good way.

I use "Hi biotch" for both men and women. Am I doing it right ?

I've actually never had a woman call be "Bro" unless she was my sister, cousin, or sister-in-law. I wonder what the context of your experience is