My 4 year old still eats non food things…. His biggest thing is paper. But he’ll sit there and chew on anything he can get his hands on.
I'd definitely make an appointment, can't hurt and it could be Pica.. sounds like it isn't exploring at this point since she's hiding it. My kids occasionally put stuff in their mouths still but usually end up pretty dissatisfied or upset with their decision.
My daughter likes to eat chalk and put metal in her mouth🙄 at this point I’ve just let her play with blocks puzzles and stuffed toys. She still puts the puzzle pieces in her mouth but it’s not as much. I’ve taken everything else away and kept it out of reach and only give her the chalk or whatever when I’m in her face. Good luck love.