I have finally go the ph swings under control but not before causing multiple deficiencies. The biggest leaves were yellowing/browning and drying out but progression has stopped for now. I have also had issues with the leaves curling up/canoeing this week. Humidity has been in the 20s and the lower the humidity, the worse the curling.
I'm not super confident she'll hang on as long as I want (70+) so I'll start flushing in a few days.