There is a Facebook group called Children's Book Writers and Illustrators. If she joins and posts that she's a writer looking for an illustrator, she will get upwards of twenty illustrators posting their portfolios to browse. Most are very good, only a few who haven't quite honed their skills yet. And a pretty big price range to fit most budgets, especially from the overseas illustrators.
ETA: storybird.com is a great place to shop for and connect with illustrators, though that is not their main function.