I always wanted a chemistry set when I was younger.
I'm just wondering, if the science sets you're looking at online look a bit naff/have bad reviews, could you make your own? Get a nice big box, a white coat, maybe a special scientist name badge, goggles, test tube rack and experiment ingredients? Notebook/clipboard for recording results? Or even those exercise books she might use at school where it's blank at the top (for a picture/diagram) and lined on the bottom for writing. They are called project books in whsmith.
At home we have done lots of cool experiments just using kitchen stuff - vinegar/bicarb volcano, mentos in diet coke, dying flowers, mixing colours using kitchen paper. Must get round to doing chromatography (use coffee filter paper IIRC), also DH has found some awesome looking ideas on Pinterest for stuff like making a cloud in a jar! You can make a hovercraft too using an old cd, a sports bottle lid and a balloon.
There's loads of great books out there for kids' science experiments, maybe ask in your library (I think it's around 500 in the Dewey system, there should be some in the children's section - I got loads out and just went through each one picking out the ones that looked fun/foolproof and then made a list of what we'd need.
It depends if she would be happy with an obviously home made gift (particularly if she's seen something particular advertised) but I think you might be able to do a lot more with a home made kit if you research it, as the commercial stuff seems a bit sterile IYSWIM?