If you want to be published by one of the large companies you will need an agent:
Actually this site also has first rate information about publishers of all sizes. If you want to go it alone join a writer's forum and learn what you need to create e-books and how to go about marketing a digital POD book. You can look at our books which are mostly POD and widely available. If you go it alone you MUST set yourself high standards for design and quality.
Buy a copy of the Children's Writers' & Artists' Yearbook for listings of publishers and agents. She could also try joining SCBWI - Society of Children's Book Writers & Illustrators. They run an annual conference and lots of events, which are great for networking.