Do NOT worry about "cutting lines"! This is something she is entitled to - and from my experience they don't require documentation beyond self reporting (I actually think under the Americans with Disabilities act they CAN'T - but I'm only Canadian so I may be wrong). I had to do it very briefly due to a temporary issue on my last trip, and I was treated SO well, and don't feel guilty at all that I got to 'cut lines' as otherwise I would not have been able to do much of anything at all. My family of three was allowed to go with me. Let them take care of her everyway they can so that you can all enjoy your trip to the fullest!