J.W.
What do you mean by medium sized pebble? Are we talking pea gravel sized cause my kids ate that all the time and other than making the poop interesting it harmed them in no way.
Obviously if it is really lodged in there you will need a doctor to remove it. If she is eating and breathing it isn't life threatening. If it really is lodged in there you will want it out before she falls asleep in case it shifts and does hamper her breathing.