Choppychan
Yamadori
I do think it's the soil that is suffocating the roots. It probably already has dead roots as a result of the soil being so compact. I think watering on dead roots might be causing some rot which is why I need to be even more careful with watering. I won't water for a while and will leave it dry even after the repot.Nice jade! Those shriveled leaves can be a sign of rot. I know you said you water pretty infrequently, but if it's too rootbound then maybe it's trapping some water deep inside or maybe just lack of airflow/ oxygen in there. You can just remove the affected leaves with no worries.
When you repot, be brave and wiggle a chopstick in deeply from every angle to break up that rootbrick. Work in your new chunky soil really well so there are no big air pockets. Leave it pretty dry for several weeks or more before you water.
These things are tough as nails so it will be fine no matter what you do to it (except overwatering, lol).
When I went to collect it the older lady who used to own it had it sitting in water. She said herself she might have overwatered it as she couldn't lift it to get the water out the saucer.
So that could have caused lot term damage which I can only fix by repotting and removing dead roots. If she's survived this long I think she'll be fine.