I have a hard time believing that an ecu would go bad, but the car would still run, I'd go the autozone route and find out exactly what is wrong with the car. It sounds to me like they are just trying to get her to trade it in. I can imagine if you went the go ahead and fix it route they would replace the ecu, and some cheap sensor that was actually the problem.
2500K@4632.1, 7970 Eyefinity 4800*1200, 2x Crucial 64gb raid-0, 16gb Gskill
2013 Subaru Outback 1994 Integra
CCNP, Working on CCVP