Nice activity to do with a 9 year old?

[Budgetating]

Something a bit random. We've had to cancel out holidays as DH is injured, but IL's are there and it looks like they may take DS for a week or two.
DD is putting on a brave face, but she's clearly a bit offended. What activities could I do with her that are a bit special. She likes swimming so I'll take her to the beach, but we often do that so it's nothing out of the ordinary. I've found somewhere that offers a glassblowing workshop, but it's only 10 minutes plus half an hour waiting for it to set so hardly a day trip!

fruit picking? Afternoon tea just the two of you? At her age, I'd go for something that feels a bit grown up.

Depending on circs, that’s awful that the IL’s would take your ds and not your dd - why not both?

If she likes swimming, is there a water park or swimming baths with slides anywhere near you? It depends where you live/how far you want to travel really.
My own 9yo dd would be bored to tears having afternoon tea alone with me! She’d much prefer something like swimming baths, roller rink, ice skating, fun fair etc but I don’t obviously know what’s open near you.

Definitely a nice hotel for afternoon tea, I took my dd at a similar age and she loved it.
Any good crazy golfs near you? If your near York they have a new Harry Potter themed one in Coppergate.

Why aren’t they taking DD as well?
Anyway, Go Ape?
Theme park
Big outdoor zoo like Port Lympne, Marwell
Cinema and dinner
Afternoon tea
Days shopping
Theatre
RHS garden or similar.

And let her take a friend! Much more fun.

Stand up paddleboarding!!!

I think if her grandparents are taking her brother and not her, and she is offended by this, anything else will feel like a second best consolation prize. I know my nine year old would be upset if her brother got taken on holiday with grandparents and I took her swimming. Unless there is a specific reason, like an activity holiday that dd can’t join in with or something.

DD is 8 and loves going to a pottery painting cafe and for lunch when it's just us.

What a shame that your ILs won't take dd too. DS is 9 and on our fun summer trips list we have the following (these are all doable as a day trip for us but might give ideas for things you have near you):
Sea life birmingham
Water park with inflatable obstacles etc, will probably take a friend of his too
Go Ape
Weston super mare (or other seaside resort with arcade, rides etc)
Warwick Castle
Pop up tent in the garden, light the fire pit and toast marshmallows etc then sleep out.
cinema

We probably won't do all these but they're our options so far. I still love spending time with him just the 2 of us but generally anything that involves inviting a friend is a winner with him!

Can you ask her?

Half the fun of a staycation is in the planning, so let her make a list of things she really want to do/try and work together to see which ones are possible.

Ideas:

Water sports
Horse riding/pony trekking
Trampoline place
Water park
Theme park
Theatre/Concert
Go ape
Aquarium/Zoo
Mudlarking/fossil hunting
Have a sleepover with her friends
Redecorate her bedroom (doesn't have to be major, but she could shop for new bed covers/lamp/cushions/some posters etc)

If you're not in London have a few days here and do the tourist things/catch a west end show. Or other city that she hasn't been to, but has a lot on.