Swimming.
Dd10 loves swimming, well, splashing about in the shallow end like a goofball.
Canal walks, spotting the boats etc.
Picnic day - go Tesco first thing, let her pick sandwich fillings and a bit of cake and whatever you can afford, go home, make it all up, put in tub and head to local park.
Lots of library's and art galleries and museums have kid friendly stuff in holidays.
Hop on a bus somewhere and window shop.
Visit a family member she hasn't seen for a while.
Or, the best day ever, tub of ice cream, chocolate, microwave popcorn and crap food like mini pasties, sausage rolls and pork pies in those 3 for 2 packs from Asda, a duvet on the sofa and she picks movies for you to watch. Eat junk and watch junk whilst chatting and cuddling up.