Unless Sara installed spy software on your iPhone. But I would think that's unlikely.
Maybe she told her parents what she had eaten and that it hadn't been easy to convince you she didn't want a children's menu. You didn't tell her background, but maybe her parents are rich enough to pamper her more than is good for her when eating in a restaurant.
Next time give her the choice from the same menu as your son, telling her that's the way it works with you. It's up to her then to refuse and prefer a sandwich or a few slices of bread at your home later.
I took my 9-year-old son and his classmate, Sara, for the weekend. Sara's mother offered to pay for expenses. I declined, stating that Sara was our guest. She kindly accepted that. During the weekend, using my iphone6, I had texted Sara's parents, sending updates and pictures. I also have Sara my phone to face-timed and talk with her parents. En route to Sara's home, at the end of the weekend, I texted Sara's parents saying when we'd arrive. I did not use the phone after that, except for the using the gps feature for driving instructions. After I dropped Sara off at her home, I drove myself and my son home; we talked about how Sara had been rude by insisting on ordering expensive dishes at the restaurants, refusing to use the children's menu. My iphone was on the seat next to me. A few hours later, I received a curt (not her usually friendly tone), seemingly defensive text message from Sara's mother stating that she would reimburse me for all of Sara's meals. Did Sara's parents receive an audio or text message of the conversation I had in the car with my child? Is that possible?

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