Or possibly a hearing aid someone posted somewhere that the first electrical hearing aids were coming out in the 20's and that sort of sizes.
why would it be a mobile phone surely it would be a communicator so would be on her wrist

Prehaps she was just one of those people who likes to talk to themsleves pretending she is on a communicator to not look mad

Nearly everyday I notice people talk on there phones when they suddenly ring or beep so plenty of people who like to so it nodays