Hard one, maybe sulfur, a yellowing or chlorosis that starts on the leaf margins and progresses inward is a characteristic symptom of a sulfur deficiency, buuuut.
It looks immobile but effecting all over it seems , makes me lean more towards iron which is still immobile, iron and sulfur deficiencies can show similar initial symptoms of chlorosis (yellowing) in plants, but the key differences are in the affected plant parts.
Iron, Yellowing between the veins (interveinal chlorosis) of the leaves, with the veins remaining green. Iron is essential for chlorophyll production, the green pigment in plants which may be why plant seems to be more effected all over.
High soil pH (alkaline conditions) often makes iron unavailable to plants, can also make phosphorus binds to iron above a pH of 7. I seen a couple purple stems too which is indicative of p shortage. Worth checking out pH make sure she isn't drifting alkaline.
Between 6 and 7, P binds to oxygen. Above 7 it starts to bond to iron instead.