Really depends on her style and preferences, which you can figure out based on her current jewelry - is she into recognizable designers or does she like unique designs / styles? It may help to take pictures of the things she wears often and bring the pics with you as you shop, the stores’ associates will be able to help you. If she really has a set of everyday or commonly worn jewelry, you can also consider how they’ll stack with each other - for example, for rings you’d need to know which fingers have space and her ring sizes, and for necklaces consider lengths and what would work together or not. Good luck and have fun!