Not sure what you mean by extra space for a disability. Did that person pay for a second seat? If that is the case it is my understanding that person can get a card from either the gate agent or the ticket counter that they can put on the seat next to them when they board.
I am assuming that person may also be eligible for a medical pre-board. Check with the gate agent.
As for the rest of you, if you didn't buy Early Bird Check In I would check in online 24 hours in advance. If you get an A boarding pass board then, if you get anything else, line up for family boarding between A and B groups.
Your child won't have to take off their shoes at security, the adults will. Visit the TSA website for more information about security.
For real life practical advice...have an adult go thru security, then send your daughter thru, then the other parent. Snacks are good, and we give my daughter either gum or a sucker on the plane to help with ears, but have never had a problem.
