I’d call Motability. You can potentially leave it with the dealership you pick the new car up from, but since that’s a different lease (if i understand correctly, you’re dropping off your partners car, but picking another lease up for your mum) it’d require notice to Motability.
At least i’d double check with them.
Prior: SEAT Ateca Xcellence Lux 1.5 TSI DSG MY19, VW Golf GTE PHEV DSG MY23
Current: Hyundai Ioniq 6 Ultimate
Next: we'll see what's available in 2028.