Quite sure the “bad” friend was supposed to be “badass” friend

Or "trashy" or "cheap" friend

No I think it was meant to be bad friend in that they likely weren't actually close emotionally and her friend probably took advantage of her in some ways which you can see in how they interact now. I think the point is that the friend wasn't the best person but in this new life she is different and capable of being a better friend, but that they wont be super close since they probably brought out the worst in each other or something

Yeah like how you call your bff a bitch but you would still kill anyone who hurts her