During lessons, she points out what I'm doing incorrectly, and we do some work to correct it. This is mostly done through scales, arpeggios and Czerny.
This in itself is worth exploring more deeply here to get to the bottom of it. For example, "incorrect technique" can be described in general ways such as - uneven playing of individual notes rhythm-wise or one louder than the other without control, tense hands hammering down chords, lack or articulation, etc. etc. A teacher might "solve" a problem by saying for example: "well, you don't have "finger independence" so you should do these Hanon exercises, and Czerny, and scales, and by "doing" these exercises that problem will get fixed. Now in this Czerny exercise, remember to make this louder than that, remember to do so and so in this measure ..." or something like that. The fact that you have a lot of corrections to remember might mean that it's going along this kind of line.
Different teachers will approach things in different ways. I can only write about things I've come across, which is mostly for myself as a student. A teacher might isolate a particular thing (or maybe together with you, or you isolate it), and decide to work on that thing - some things that are at the root of a problem and its solution. It might be a stiff wrist, and why is it being kept stiff, and what kinds of things do you need to do to turn this around - and then a way of practising that, and things to practice on. You might get only a few few instructions, and smaller repertoire to work with.
I returned to violin this year after being away almost a decade, and I had major problems when I left. One of them was a kind of lack of dexterity: once I put my fingers down I couldn't lift them off anymore and I had had to give up one piece because I simply could not play a passage. Well I learned that you don't have to push down very hard on the strings, and if you do so it locks up the hand (piano has the same principle). So I practised one simple thing - pushing the strings lightly just enough to make a good sound - that is the only thing I focused on. Some time later I came across that "impossible" piece with that "impossible passage" and it was ridiculously easy to play. The problems had had a particular cause, and by addressing the cause, it stopped existing.
As an example: On piano when I was self-taught I followed bad instructions from an old book for playing scales. I stopped back then when my hands went numb and started to hurt. Later if I tried to play scales, everything I had trained myself to do would kick in. So we have gone at this in stages. I had learned to "snap the thumb under", and had motionless hands and arms with just the fingers doing their thing. The thumb muscles would tense up getting ready as soon as I had played the 3rd or 4th finger. So I played 3 notes, stopped, brought the hand over to its next position while keeping the thumb relaxed - and gradually transitioned. It was one new habit at a time.
Another thing which takes a lot of patience and trust is working on what can be changed right now, while accepting that other things might continue to suck for a while. And just keep chiseling away here and there. What you do with your hands may affect your shoulders positively; what you do with your shoulders may have an effect on your hands. How you balance your feet may affect what your back and arms feel. So you keep experimenting, and any time something feels better and seems more effective, you have gained ground.
My problem then arises when I'm practising at home, as I struggle to remember all the corrections and apply them all.
There may be too many instructions and too many corrections. (Which is why I gave the violin example where I focused only on "light touch" for a while.
My other problem (which is more something I just need to deal with) is that I find it hard to motivate myself to play through the Czerny, as it's quite dull/repetitive.
This suggests that you have not been taught how to practice, or don't know how to practice. If you are "playing through" anything - especially in view of fixing technique - then you're not doing the right thing. When you have Czerny as a means to help you, there should be a specific thing for you to focus on, and that thing can become fascinating in its own right. I do not agree with the mentality where particular etudes are supposed to magically fix things by dint of doing them (and that mentality does exist). I don't know if you are actually being guided.
With the rsi, on my own I went back to playing much more basic pieces (mostly grade 2 or 3), and my teacher said it was even more important to keep doing the technical work to correct the issues.
Do you mean that in addition to you playing basic pieces your teacher wanted you to do the other things (i.e. Czerny, scales etc. = technical work?). The basic pieces themselves can
become the vehicle for technical work. Because the material is easy, you can put your energy toward the actual physical motions and sensations. The goal is (I think) motions which create greater ease, sensations that feel good, and sound which sounds good - as three points of focus.
Topic: Trying to retrain hands...