Side/window Air Bag problems of the 2012 Ford Edge

Passenger air bag turns off and then back on after from one to 30 minutes or more while driving dealer-no trouble found. Reported multiple times. Dealer finally replaced sensor module 2/17/14. Was better, but still failed when my friend who weighs 110 pounds was in the seat. Dealer replaced passenger seat tracks on 5/19/15. Better, but still failed. Back to dealer on 6/17/14 and again on 9/18/14. Finally said the system was working as designed even though my friend weighs 110 pounds. The owner's manual says that the air bag should be off when the seat is occupied by a small child. My friend is not a small child and always wears her shoulder and lap belt. The system worked perfectly for the first 29,000 miles and then started failing. The bad part is that the side air bags are disabled anytime the passenger air bag is off, thus she would have no protection in any kind of a roll over accident. The final words from the dealer are, "unable to find any problem with the system operation. Occupant determined to be small in stature causing system to deactivate. Reviewed with fse who is in agreement at this time". This is certainly a safety problem that should be addressed. The dealer won't say, or can't get any answer from engineering as to the minimum weight in the passenger seat to activate the air bag system. There must be a spec that all cars must meet.