Another question/concern for me: if I restore an old picture of my Gramma, will my Gramma (or a Gramma that looks strikingly similar) ever pop up on other people's "give me a random Gramma" prompts?

It might show her for prompts of “show me the world’s best grandma” :)

On free tier, I’d essentially believe that to be the default behavior. In reality they might simply use your feedback and your text prompts instead. Certainly know free Google/OpenAI LLM usage entails prompts being used for research.

Edit: decent chance it would NOT directly integrate grandma into its training, but would try hard to use an offline model for any privacy concerns