Hi Jon, don't know where you're staying.......but try spending the day at Kaloudis pool (Splish Splash) there are always plenty of teenagers in the pool there, so I am sure she won't mind her old Dad joining the oldies at the bar while she makes friends.
Everyone who has done the pony trekking has enjoyed it, you don't need any experience to do it. Also there is usually a good age mix too.
Hire a boat and visit a couple of the small beaches around Arillas but take a picnic and plenty of water.
Another good one is to learn wind surfing in San George a little more expensive but
when we have watched them everybody was having great fun.
You know she just might enjoy "Me Time" with her Dad doing the things you always do in Arillas...... so ask her.
Val x