If she does that I think it will confirm her narcissist personalityI have a horrid feeling the Scott post is Carrie building up to dumping Joel, so she feels like she's balanced out her heartbreak.
She was infatuated with someone but got dumped; she felt powerless, so she needs to dump someone who's infatuated with her to feel "powerful" again. It's a cruel move, but it's typical behaviour for someone who needs narcissistic supply and ego balancing.