In reply to kathrync:
Thanks all,
She has a Galaxy tablet, which is quite locked down (limited internet access and no social media), but I'm sure her parents will let her put a photo editing app on it. Good call on making sure it's easy to transfer photos.
I was really looking for specific suggestions, so thanks to Iamgregp - that looks like exactly the kind of thing I'm after.
Jenny C, yes, I got a basic film camera for my 8th birthday. I loved it - one of the reasons I'm keen to get something for her. I was lucky because my Dad is a keen photographer and always had spare film kicking around, so I rarely had to pay for it.
Regarding the instant camera, refills for the system I am looking at are 14.99 for 20 prints - that's the cheaper end of the market. She gets £20 pocket money a month. I certainly wouldn't spend 3/4 of my monthly salary on film, so I'm not sure it's realistic to expect her to do the same!