It's important to note that Anne was a young teenager during her time in hiding, and her diary reflects her daily life, her anxieties, and her hopes for the future. While she enjoyed reading, it's more likely that she read books and stories that were available to her in the limited environment of the Secret Annex, which may have included contemporary literature, classics, and possibly some children's stories.
It's possible that Anne did encounter Greek mythology through other sources, such as her education before going into hiding, or through references in other books she read. However, there's no concrete evidence to support that she actively read Greek mythology.