he should be fine. we had a large group (like you will) on a flight to vegas for my sisters wedding and my nephew (18 months) was fine he too was the only child on the flight. we let him roam and go around talking and sitting with everyone that was with our group. He had a blast. But yes a dvd player or toys will help too. On the way back he slept though just abt the whole flight. again on our flight to arizona he was fine too did the same we didn't make him confined to his seat only when it was mandatory. She shouldn't have any problems.