Before any sheet music is introduced, a proper method book should be purchased and gone through page by page. The method book will show all note fingerings and embouchure directions that will enable a beginner to be successful at playing her first song. Without the method a beginner could become frustrated and discouraged.
"Essential Elements" is a series of books for beginners that has recognizable melodies within, but also incorporates exercises, scales, and long tone studies.
Once the student is able to make notes quasi-consistently a step-up book will be required. "Basic Studies for Flute" is an excellent choice, which will help develop a consistent practice routine.
When the player is ready to move on to pure sheet music it is important to find recognizable melodies that will give the beginner confidence. Songs such as "Mary had a Little Lamb," "Twinkle, Twinkle Little Star," and "Happy Birthday" are some examples. Below are links to sheets music free for printing. There online sites such as Fluteinfo.com that have free music from composers such as Bach and Telemann for download and printing.