If she hasn't ridden in years, I think I'd focus on balance first. Lower the seat so that her feet touch the ground, and take the pedals off the crankarms. Ignore gears for now, and keep braking instruction minimal, just enough for control (rear only?). Have her practice "scooting" with her feet and towards lifting them off the ground to coast for longer and longer distances, all while balancing the bike. Once she's got the balance and steering parts nailed down, then re-install the pedals and work on pedaling and braking. Shifting can come much later, and the seat can eventually be raised.

Good luck, withm and neighbor! You'll do great!

(Sorry this sounds so abrupt- running out the door!)