A cool and (relatively cheap) present you could buy her is a hand lens. Like this for example. That one in particular is quite expensive for a child but you can get them for less than £10.

The reason I suggest it is because it is a good way of learning how to look at things in closer detail. It also means that she can pick up any rock she finds (for free!) and analyse it in a bit more detail.

For example, a simple thing to do is look at sandstone with a hand lens. Suddenly it becomes clear that one rock is lots of tiny rocks! How are those tiny rocks held together? What shape and size are they? Are they all the same? etc.

Basically, something straight forward can become a whole lot more interesting!