No offence, but it's not much of a picture, is it? Something face on, close up and clear would be a lot more helpful.
Is it kept in the metal box? If so, I'm guessing the metal box is a match safe repurposed to keep the figurine in.
The figurine looks to be St Joseph (or possibly the Virgin Mary, it's hard to tell from this photo) holding the Christ Child. Was your Nan a Catholic or had Catholic relatives?

I'm thinking more like St. Christopher, who is usually depicted carrying the Christ Child and is the patron saint of travelers. My mother always wore a St. Christopher medal, because we traveled a lot and in fact, I think I buried her with it for her final journey.

Seems to be a miniature personal religious "pocket" statue.

Look at the linked Google images for similar items.

Here is a link that might be useful: Pocket statue images