Piano may not be this student's tool for finding life's deeper truths. It may be that piano and playing those favorite pieces gives her a sense of accomplishment which energize her to find truth on her own path.
Oh, well formulated!
I am one of those adult hobbyists/hobbits.

I have started to take lessons again, after 29 years of no lessons, and I enjoy every moment of it. OK, so the main reason was not that funny; I felt I started to injure myself so I needed help with my technique. Someone watching me play and helping me correcting my posture etcetera.
As I see it, I don't pay my teacher to teach me how to sight-read certain pieces, and certainly NOT to motivate me. That is MY job.
She has asked me several times what my goals are and I cannot really figure out, we try to find this out together. Right now I think the simple answer is that I love to learn, to accomplish things, and I love this music. I have attended concerts during a few years now - of course I did that in my teens then, but that was different - and I have been more and more touched by the music, until I started to feel euphorical by some performances. I can get tears in my eyes with emotion, something that never happened before. (Ok, so I have grown sentimental.

) And as I DID study piano myself, I could appreciate and admire the performances fully, I think.
And then I wanted to participate myself so I started to play again and today I find it most satisfying and thrilling to have this wonderful music "in my own hands", to learn those things that seemed so difficult and challenging ... It is such a kick to sit down at the piano and be able to play what I used to just

at before ...
Do I want to become a professional? Or a teacher? No, I don't think so, because I have other things to do in life, I think there are better ways to make a living - I'm a novelist and a technical translator - and I am really not very fond of performing, I have always suffered from stage fright.
But I DON'T like to restrict myself either. I want to take my piano work as seriously as you can. No, I see no exams, no competitions (I guess they are just for young people anyway) and no serious recitals ahead of me. But still I work "as if". What I love the most with my lessons is that I am also treated that seriously. Yesterday we worked with ... the G Major scale. Why? Because she wanted to work with some technical issues, some wrist movements I have to practice. Then we worked with the musical expressions of two pieces I am about to perform in her little "student gathering" in a few weeks, we discussed different interpretations back and forth. "Try not building up that crescendo too fast", "what does this phrase really mean to you" and so on.
To me this is GOLD. I cannot discuss these things with my family here at home, as I'm the only one playing the piano. In fact, I have noone to discuss with at all, noone who can give me feedback on any kind of expert level. In my lessons, I feel like a concert pianist.

Or at least like a real professional. Serious business in order to reach "perfection". No "that is not for mortals like you, my dear" or "it's too late for this and that" or "how can I motivate you to practice more?"
Simple technical exercises are sooo flattering when you don't feel that you have to do them because you just cannot to anything more advanced. She knows I can play a part of the Appassionata, so if she thinks dealing with punctuations in the G Major scale is the thing to do NOW, I feel very content with that.
So, even though some of you would call me the Great Pretender, I love this feeling of my lessons. I feel inspired, because I am treated as a pro, not a lazy amateur who cannot make up something better to do with her spare time, or a better way to waste her money. My teacher also says it is so inspiring to teaching adults instead of school kids, because the adults are there because they really really want to be there, not because their parents have forced them to go there ...
I can only speak for myself, of course. So, how to treat an "uninterested" adult student? Maybe by encouraging them to raise their own limits. They want to learn a pop song? Then treat them like they were Elton John. (Without making them divas, of course. If their play sucks, then it sucks. Tell them it sucks, like Elton John's manager would tell him the same.) They start playing at the age of 38 and dream of becoming the next Rubinstein? They don't tell them "sorry, it's too late for you, it is not possible, and besides you don't seem to practice enough." Start working instead, assuming they WILL reach this goal (at the age of 130).