Managing overtalking staff, and some more.

Kind of venting, but also curious to hear others' thoughts and experiences. I am taking on this new report, who is brand new to the sales department. She came from QC and worked there for seven years. She's fantastic and very proactive at QC, all sales love her (because put plainly, she's simply useful). Now, mid-career she changed to sales and many explicit and implicit aspects are new to her. I have no doubt she will learn the facts in a blink but it is the social/tacit/unspoken aspects that's challenging. I must highlight the fact that there is a bit of a on-the-spectrum thing about her, the "Extraness" is the first thing you notice ,but it also blended very well into the high energy/proactive behavior at QC. Another minor detail is that she's not American (Slavic), and English is not her first language.
Now, at sales, two observations that I have issue with. 1. she can't seem to stomach that I am now her boss, 'cause she's been with the company for longer than me and used to provide me help, now the dynamic reversed. So she makes a point in client meetings that I am her "partner". 2. anxious overtalking and overexplaining. she does not observe the typical conversational etiquette of turn-taking, it's always like talking to someone on the phone with bad connection so both of you end up fighting for airwave, and as soon as I pause to think, she's continue on and on to over-explain (this is sign of high social anxiety, "on the spectrum"). On client calls, she does the same.

Now about the acknowleding I'm her superior part, I am not one of using title to exert power, but it is at the same time disrespectful for me, when she clearly needs a lot of training and help on sales but can't get off her ego horse. I am going to find a light-hearted way to remind her that I am now her boss, this is not a big deal at the moment.

The overtalking part, and won't let people finish, and won't let silence happen, is becoming truly exhausting. An additional layer to this problem, is that she echoes. She has no original thoughts or solutions (or at least did not have the courage to offer them), but almost EVERYTHING I say, she immediately echos it back and adds her redundant extension, the tone is like she had always known/these has always been her ideas, it literally want you to say "would you just shut the F, up". Note that every feedback I or our mutual boss have provided, no matter how neutral or gentle (our boss is quite laid back and gentle, anybody with a brain and basic social skill would find it very amicable. She barks right back and gets defensive, it makes her appear that she can't do wrong and how dare you pointing these out. I am one week away from concluding that this person simply is nuts. I have not formally sat down to address the overtalking and echo part, because admittedly, it is very subtle. She is technically not "cutting me off", so I can't say "let me finish", but, there is not even a 0.5 second of gap between my speaking and her echoing. The echoing thing, she may well think it is a form of flattering, it probably just something I have to swallow as it's not "Wrong".