Hi M.,
First, I highly recommend asking your daughter's teacher for her thoughts/recommendations.
Second, I will offer my own recommendations as a first grade teacher.
1. Scholastic publishes a series of "Hello Reader" books, with levels 1-4. Level 1 for the beginning reader are good. In general, you will want to look for minimal text on each page (maybe 1-2 sentences per page) and big and colorful illustrations that make the text predictable.
2. If your school sends home Scholastic Book Clubs, you may be able to ask your daughter's teacher for recommendations on which books would be most appropriate. There is a list of book levels that the teacher may be able to access to help choose narrow down which books would be most suitable for a beginning reader. A local librarian would be able to help you with this as well.
2. Choose books that have a predictable/repetitive pattern, are familiar songs, or are rhyming books. Children often "pretend" read first, making up their own words before actually reading words. Later, they make the connection that words are written and we actually read them.
3. Many times, more than anything, I think establishing a good reading routine is what beginning readers need - and this can be done with almost any book. Basically, read, and re-read with your child. First, do a picture walk - tell the story through the pictures. If there is a picture of a dog, see if she can find the word dog on the page. With picture walks, you teach her to use picture clues and match them with letter sounds that she knows to infer a word that she might not actually know. After a picture walk, read aloud the book to your child. Maybe reread that book 2-3 times to your child and then let her read with you (shared reading). Ideally, after 2-3 read alouds, she will have memorized some of the words and putting that together with her knowledge of letters and sounds, she might be able to read bits and pieces on her own. Eventually, she will be able to read that book independently (even if it is mostly memorization, but this is the first step in becoming a more independent reader).
4. Some of my favorite children's series for kinder and first grade: Froggy, Frog & Toad, Morris & Borris, Arthur, Franklin, Clifford, Henry & Mudge, Amelia Bedelia. Some favorite children's authors: Eric Carle, Kevin Henkes, Dr. Seuss, Jan Brett, Eve Bunting, Bill Martin, Jr.
Good luck!