It does look like over watering, if your roots are going to rot they wont take up the nutes and she will yellow off. Potting down is an option but since the roots will go outward and down first that could be risky. You could be drying out due to temps and airflow evaporating off the top of the pot rather than her drinking it. Test the weight. I use coco so please forgive me if I'm wrong, soil should still weigh a shit heap less when she needs a watering.
Can take along time to recover from over watering if its gone on a while.
You are a little cool temp wise though so maybe turn the fan down or point it lower down so the air flow is still good but less harsh. That might raise the temp 3 degrees!
Good luck with her.
C.W