Do you have a syringe? You could try holding her in your hand and back flush her gill. I am assuming she "ate" the gravel and it got stuck in her gill as it tried to pass. In that case, you would want to flush from the outside in. Be sure to hold her vertical so the gravel will (hopefully) fall out. Of course, be gentle. I would look it over closely before attempting to remove. I would definitely try to take it out the way it came in, versus forcing it on through.
Good luck!