There are folks who hang out here who can give you all kinds of info about your treadle. (I'm not one of them.) You'll need to take a photo of the sewing machine, itself, and post it for someone to help you to the next stage. First, they have to figure out what brand it is, then hopefully, what model number it is. Then, what needs to happen to get it to sew again.
Take a good, fairly close photo of the sewing machine from the front, the back, the top and each end. Just get it in some good light and use your phone or whatever camera you use. If you have any trouble posting, let us know and someone will help.
Congrats on getting your ggrand's sewing machine. I have my mom's 15-91 and wonder whatever happened to my grandmother's treadle.
bkay