Only way to know is to put it on and see if it fits. It's not just the foot, but the part that hooks onto the needle clamp screw.
The super old rufflers were made for machines with a different type of needle clamp screw than many modern machines have (way smaller) so they are not wide enough to fit over it. Some machines were different enough that they needed a specific ruffler - sometimes that arm needed to be longer or shorter so it did not unhook when the needle was all the way up, or jam when the needle was all the way down. Some had to be bent as the needle and foot were off center from each other.
Knowing what machine your grandmother had would help. Only a very few (including Singer) were side clamp feet like modern machines are, and if hers was a top or bar clamp style (White, New Home, Free, Standard, Domestic, National, Davis (and many others) including all the badged names these companies used - it will only fit that type of machine.