Consider ice skating if your daughter likes that. There is a rink at Somerset House which is a lovely location, and you could combine with a gallery visit inside if you have time. Best to book online but you can also get walk-up tickets when it's not rammed. It's easy on the Tube to Temple station, quick change at Baron's Court.

There used to be an ice rink at the Natural History Museum but sadly that is no longer. The museum itself is definitely an excellent (and free) activity option anyway, and even easier from Heathrow.