A surveyor measures a point once and then works to the record. A character deserves the same discipline. Described from memory at every job, she is re-measured by mood each time — and every re-measurement moves her a little. Written once into a survey card, she is measured a single time and every tool at the table works to the same figures.
The card holds five measurements in fixed order. Age, a plain number. Hair — colour, length, habitual style. Build in two or three words. Face — one or two enduring details. Signature — the detail that identifies her in a tight crop. Everything else — outfit, corner, hour, light — goes in the field line beneath the card, and the field line is expected to change with every sitting.
Paste the card word for word at the head of every prompt. Generate at the standard cost of 6 credits, keep the best third, and let repairs, swaps and upscales touch only what judging has passed against the recorded measurements.
Drift is not a model problem. It is a records problem. Keep the record, and the character holds.