Check out reviews online. There are many book blogs and review sites that can give you an idea of which of her books might be the best to start with based on your interests. If you like vampire stories, then the 'Blood of Eden' series could be a great starting point. If you're more into faeries, then go for the 'Iron Fey' series.
You can start with the first book of her popular series. For example, in the 'Iron Fey' series, begin with 'The Iron King'. It will introduce you to the unique world she has created and the main characters.
Visit your local library. Libraries usually have a good collection of her books. You can browse through them, read the blurbs on the back, and see which one catches your eye. This way, you can start reading her fantastic fiction without having to spend any money upfront.