Thanks Calluna and thanks all for the ideas.

I ended up getting her a voucher to a day-spa. She's going camping for 3 weeks over summer so I bought her a voucher to a place near where she's camping so when she's in desperate need of a shower and a comfy lie-down she can go spoil herself. I was a bit sad to not get her something special to keep as it was a milestone birthday, but she seemed stoked.

Oh, and Olive, I looked up Hard to Find. Ooooooh such lovely stuff, thanks for the tip!