Jim thinks this is just before WW1, making Justontime's grandma early twenties?
It would fit with the "nanny" hypothesis, except, of course, that she worked in a shoe factory, you said?
It's an odd photo, isn't it - with the exception of the smiling girl in the back row and the woman on the right, who has a pleasant expression on her face, the others look either puzzled or downright bored. Your granny also has the air of being in the wrong place, somehow, do you know what I mean?