It might sound silly but have you ever thought of purchasing a treadle machine off of craigslist? I see them on there for under a hundred dollars. Lots of people love the rhythm of them PLUS she could control the speed.
There is a vintage sewing machine shop on this board. Lots of people on there sew on them and teach their grandchildren. Here is the link...
http://www.quiltingboard.com/t-43881-1312.htm#3693961
There are tutorials and youtube sites to learn how to use them. Pretty easy actually.
:-D