I have to agree that a used transmission is too risky. While the yard probably offers some kind of return policy, (usually 30 days), a transmission isn't like an alternator. In other words, if the used one was bad, you would be out the labor cost of the swap. Of course, a rebuilt is expensive, (around 2,000) so you have to weigh the options of the rebuild verses trade in or private sell with rebuilt transmission verses non-working transmission. She might also consider rebuilding the transmission and keeping the car a few more years. The way I look at it, if the rest of the car is in decent shape, a rebuild would be the way to go and stick with the car a few more years as you know what you've got verses a different car that might have issues you're unaware of.