I virtually live in Heathrow T5, there is no official pickup parking which is free. you will have to pay short stay, but Its proper easy, probably the best airport terminal for drop off and pickup.
Although if you know exactly when landing, i would loiter somewhere around the heathrow complex and get your daughter to text or call you when she has collected her luggage and collect her from the drop off on the top deck of the parking. This is officially not allowed, but at 10:30PM you will be fine, i wouldn't wait longer than 5 minutes up there though.
EDIT- Just saw she is travelling with no luggage, so get her to text when she gets through passport control. She will be about 5-10 minutes to the car park from there.
