Hi there. I am in need assistance with assessing a friend's behaviour and potentially helping her to get out of it. Forward disclaimer, I am familiar with this sort of issue and am able to detect it due to experience from high school, where two people, one from school and another from a social circle displayed it. However, kids tend to have a variety of issues in their developmental phase and tend to get over it eventually. This is different. My friend is over 30 years of age.  
In attempt to briefly summarize the situation, here's a little history first. About a year ago, I've met a somewhat pleasant person who was kind enough to help me out of a rather rough patch by giving me work. Since then we've stayed in touch and gotten rather friendly to the point of having contact on a daily basis. One thing that always made me distance myself is having nothing to talk to her about. She was nice enough but seemed to lack any sort of creative capacity, past, present or future thoughts. Like the perfect definition of a *tabula rasa*. Seeing how we had to spend time together due to work she gave me, and me having the inexcusable urge to always have a conversation going, I just filled the uncomfortable periods of silence with random things that came to mind. She was super happy to listen and get involved in discussing these things, no matter how ridiculous.   
One day, due to some leftover hours since the work was done sooner than planned, I suggested we watched some TV shows I was behind on. She happily obliged. And over the next few months it became our one thing in common. We started scheduling new shows, movies or documentaries every day even after I was paid for the job. All fine, even enjoyable at the time. Although every single time I tried to ask her about her own life, I came to a wall. Not the kind where you think that something super bad probably happened and is difficult to talk about. No.  
She is the only child of two great parents who did office jobs their whole life and are now retired in a wonderful countryside home - and she visits them every week. Saw photos, it looks amazing. But it also appears to be her one adventure in life. In fact, the most miserable she ever remembers getting is a ticket salesman forgetting to give her change. Being from a polar opposite of a background and having an annoyingly turbulent life, I felt somewhat envious of her, which I was happy to express. This claim seemed to make her giddy at that time.  
Over the months, we spent more time together, I brought her to a couple of gatherings to just liven up her week a little and she met a couple of my friends. All of them immediately told me how there seems to be something really wrong about her. I've explained how she's super introverted and left it at that. However, as time passed, this always-beige, motionless lady started changing. She obtained similar clothes to mine (not getting into details, but I have a really particular taste, from materials used to colour combination and decade authenticity), started using my own jargon which is often super unfitting as I try to make a point of using the most robust synonyms I can think of in the moment, and even inserted gestures I commonly use to embellish conversation with physical motion.   
The moment I got worried is when I noticed she started copying makeup ideas I've shown online, on a website I know was never shared with her. Today, hours prior to writing this thread, she sent a message that she's enjoying a dinner... a dinner I've posted in an instagram comment to a different friend she hasn't met. A dinner that I was eating earlier today.  
So, reddit. Does this behaviour have a name and how does one battle it? What's the best way to deal with it?  
Thanks.