Yes, her interests are extremely broad within basic science. She really has only just been exposed to science; it has never been a school subject for her until this year and the news I received from my parents was just that she came home very excited during the first week of school because she would get to learn science. In the time since, her interest is disappearing because of the factors I mentioned in the OP. My goal is to get gifts of a variety of styles so that hopefully at least a few end up helping her explore her own interests and decide what those interests are.

I can't help but be reminded of John Holt and the unschooling movement. He argues that children are naturally curious, and that given time and freedom they will develop their own strong interests; the role of a concerned parent or sibling is to provide opportunities for them to develop interests, and to facilitate whatever interests they develop by providing resources relevant to them.

It's really sad that schooling destroys children's curiosity (I don't believe that schools that emphasise the science curriculum are significantly better in this regard than the school your sister attends). Given that she does attend school, your idea of getting her gifts in a variety of styles to provide her with avenues to explore and develop interests is (imho) just the right thing to do. Some technical Lego, Meccano or a chemistry set would be a great gift with that end in mind, assuming your parents are willing to help supervise her when you can't.