OP i'm so glad you guys worked it out, it sounds like you did a great job on this one! :)
*raises hand* i'm the one with the euphonium addict mother, but there is more to the story.
My mother was the 3rd of 4 kids, two older sisters (the eldest of whom was terribly damaged at birth, lived in an institution and died age 18), and a younger brother (who died age 2 when mum was 5, of a choking accident in his highchair).
So the older surviving sister was given piano lessons (which she didn't much want). She skipped class, didn't practice and wasted the money her (of modest means) parents spent. My mum wanted desperately to learn piano, her mother refused to spend the money because of how her sister had wasted it.
Fast forward...i was 8. My parents called the school and said they'd like me to try some instruments (i had no objection or preference -i didn't want to learn an instrument and yet was curious enough to want to try new things). I tried the flute. I could get a sound out of it, but had no particular affinity with it. After 2 lessons my teacher suggested we try something else as i was obviously having issues. I should say here that my father has Aspergers, amusia and SPD and i had both the latter but have mostly outgrown/overcome the SPD, but my mother was very musical, in a choir etc. Whenever my musical inabilities shone she made excuses, got mad or insisted i needed to try harder, i think she died thinking i could have cured my amusia if only i'd tried "properly". I moved to saxaphone, for 6 weeks i played it, then i wanted to quit and the teacher agreed with me, again, because it's quite hard and boring to play an instrument when one is tone deaf! I could read the music. I could play the notes. I couldn't particularly hear very well what i was playing, i could learn the notations but never remember how it was meant to sound even after many many playings. A few weeks later i was taken, with my class, to the brass room and given a trumpet to try. I couldn't get a sound out of it, but the tenor horn i could. That night i was informed i would be having horn lessons weekly and "not quitting this time". I vividly remember feeling nauseous with dread, sobbing for hours and begging my older siblings to help me convince my mother to not make me. They tried and failed.
For 6 years i played. I learned pieces up to grade 5 or 6 level but never sat my certificates because the first part of the exam was to sing a note played on the piano, and i could never do it, and nor could i tune my instrument. God knows how my poor teachers coped teaching a musically impaired, unwilling but conscientious child year after year after year...they weren't paid enough! I asked to quit at least once a year. One teacher, after i failed a trial grade 2 exam due to the piano/note issue, called and told my mother that after 3 years i was making very little progress and was not suited to the instrument. My mother merely insisted i practice an extra 4 hours a week. She had a way of asking what i wanted to do which guaranteed i gave the answer she wanted to hear. She never hit me, she barely shouted at me, but i feared her and her disapproval. I was once even convinced to join her choir so she could have the youngest daughter in the "adult" choir when i was 9. She said i "sang like a lark"! SERIOUSLY. Then after a few scores of my tuneless warbling she made up an excuse and took me home again, bathed in shame.
Eventually when i was 14 i just decided enough was enough and i HAD to quit, it was wasting hours of my life i wanted to spend studying, with friends, horseriding (which i was actually GOOD at). I made no technical progress beyond being able to read more complicated scores from age 9 to age 14. I never got a sweet sound out of it. I never played anything not mechanical and dead sounding (i am told). I never had a moment of joy at being able to play it. My teacher gave me a relieved smile when i said i wanted to quit, and told me to leave my (hired) instrument in the store room and that was that. Mum was in a bad mood with me for about 6 weeks (she bore a powerful grudge) and then it was never mentioned again.
As an adult i can see that 1) she "gave" me the lessons she desperately wanted but never got, 2) she refused to let me quit to get back at the sister whose quitting cost her HER chance at playing and 3) she decided at some point when i was a baby who i was and what i liked and even quite startling evidence to the contrary didn't phase her. Horseriding was a true passion for me, and yet she never saw me compete or even jump at home, she watched a few lessons when i was little and that was that. She was not at all proud of or even interested in my very real achievements there. Ironically i tried to please her until i was 18 and then quite suddenly i stopped. She was VERY angry for about 3 months, but i was away at university so i only encountered her rage once a week on the phone. Then she got over it and decided that actually she liked the Real Me much better.
I learned so much from that experience. When i see something my kids might like i make sure to figure out if it is for THEM or for me. I pay close attention to what DD is *actually* interested in/good at, rather than what i think she will/should be (like when we went to the beach and after i asked 3 times i realised it was ME who wanted a ride on a donkey, not DD!). I would never press my child to do something they hated, and if i feel the strong burning urge for them to try or do something i examine it closely to see if actually it is ME who wants to do it.
My mother would NEVER have offered me the chance to pay for the classes instead of going to them, because she knew i would do so gladly, gratefully, in a heartbeat. I really, seriously, wish she had just bought HERSELF piano lessons.