What are some websites that have the actual poems that Mary Shelley wrote?
Mary Shelley is most famous for writing frankenstein, so many websites only mention her novels. It is difficult to find a website with her poetry on it.
You are correct in stating that Mary Shelley is most famous for Frankenstein. Shelley was most notably a novelist. But, to answer your question, she was not necessarily known for her poetry. Her husband, Percy Bysshe Shelley, was the one whom was recognized for poetry. That being said, Mary did write poetry and here are a couple sites that speak of her poetry.
As much as I dislike Wiki, the site is good for listing of authors' works:
Go to #10- Poems- There is a complete list of her poetry. After, you can research her poetry by poem name instead of looking for her poetry under her name. I found this to be much easier when researching the answer to your question.
Keep in mind that you are searching for poems by an author known specifically for one text. It may take some determined research on your part to find exactly what you are looking for.