Your child will let you know if the book interests her. You can also get advice from the children's librarian at your local library or from teachers of young children. They can share with you lots of ideas about what interests young children. Don't worry about the level of difficulty. When choosing books to read aloud to your child don't worry about the level of difficulty.
Children readily add words that they hear to their vocabulary.
When they hear you read aloud the context and illustrations help with understanding. Also you are there to question them for comprehension and to answer their questions. Just hearing an adult read to them provides young children the opportunity to learn how stories take shape, how writers use words, and how adult reading sounds. When you read books that are non-fiction you are providing them with information about the world. Let your child be the guide.