my daughters car will not accelerate past 20 mph?

Not sure. Could be a transmission problem, could be the EMC. Is the check engine light on? That would certainly narrow down the parts purchases.

This is a few months late and you may have figured it out already, but this happened to my car (Hyundai Accent 2005) and I had to completely replace the transmission. It was super expensive and my car is having different problems now not related to the transmission.