Ummmm why would they make high efficiency units then. Maybe her unit was oversized. High efficiency units do work but usually ain't worth cause you don't really gets your money worth unless you just got it like that. Sorry but that makes no sense to me
Cost vs seer rating is finding the sweet spot
Yes, r22 ain't made no more and parts aren't made for them anymore, whatever is out there now is only available. 20 yr old system yes needs to be replaced, already will be way more energy efficient and cost less to run