It is 135cm or 12 years so they do need to be quite tall. My DS is 7 and out of a seat but he is close to 140cm. So if she is shorter than that she will need a booster. Pity you are not flying into Edinburgh or Glasgow as you could have had ours!
Thanks! We have two fold up booster seats, so will take those, and my friend is going to borrow one for the baby and meet us at the airport with it. So all sorted!