No option to turn on shared photo streams

My mother still has an iPhone 3GS (I'm trying to get her to upgrade but she's in no rush) and I'm trying to share a photo stream with her. As far as I can tell shared photo streams should still be available for 3GSs running iOS 6. However the option to turn on shared photo streams is not there. Am I missing something somewhere? I don't see anyone talking about this issue and I also don't see anyone saying this option isn't available for this device. Any help is greatly appreciated!