couple of suggestions that no one has mentioned. Ask to look at the phone and disable it secretly. I don't think a 7 year old has mastered to skill to be that techy. Maybe?
Second...they make a device that with the push of a button disables cell and wifi communication completely in a certain range. her on the phone and chat about how you wish she was in the same room with you making cookies we do at Gramma Camp here every summer...we have electronic bans...We have a time before dinner when they can use their devices to call home or check their messages...then all electronics are put on a table and we are all back outside. Seems to work!!