I would suggest an older Singer Featherweight. It's portable, simple to use (goes forward and back) and has feet for everything, including free motion quilting. They are easy to service and find parts, i.e. needles and broken lights, etc.
Check the board here - there are lots available at a VERY low price. Additionally, there are a lot of folks out there who use them and can help train her in how to use a machine. If she really likes it, it has held it's value so you'll get your money back out of it as a trade-in down the road.