Many people chatter non-stop, when they finally have an audience. I know someone like that, bless her heart! What worked for me, was to give the person a few minutes of quality listening and then move on, to another person. When Chatty interrupted, I'd just keep giving the other person my undivided attention. Eventually, I'd get back to Chatty for another dose, then move on again. She was more than happy to just keep chattering away to herself, just in case anyone was listening.
I agree you should give this new person another chance. She may be very insecure and trying to impress everyone, to gain acceptance. Is there anything you
do like about her? If so, point it out to her and maybe she'll stop trying to bombard you with all the other stuff. If that doesn't work, then try the "listen, ignore, listen" approach.
If she truly is a narcissist and is only there to talk about herself, she'll probably end up leaving on her own, if she's forced to share the spotlight.