I'm still glancing at that photo from time to time and I'm going to be silly and add in another two penn'orth.....
I'm with Ann in thinking she's about 20 (her face and her blouse). I'll stick with my surmise and think she's just been awarded a prize. She wasn't expecting to and it wasn't a public competition otherwise her hair would probably not be so simple and demure (is it even parted?).
She was caught unawares by the photographer. The necklace had just been placed round her neck and she was asked to turn her face towards the camera - hence the fact that the medallion hadn't been adjusted properly and would account for her body (the blouse's buttons) pointing in a different direction.
Right, that's off me chest....
Funnily enough there's a photograph on the web that bears an uncanny similarity to Ann's great grandmother's. On this page scroll down to near the bottom and the 8th photo down is a young lady standing by a pot plant. Spooky.....
Code:
https://blog.findmypast.co.uk/family-photos-what-are-they-wearing-1406240689.html