the Hebrew name usually associated with 'lily of the valley' is Shoshana (from the Hebrew word 'shushan' meaning 'lily' or the modern translation of 'rose'), the English version is Susanna or Susan or other variations of the name.
However, the plant that is typically called 'Lily of the Valley' today is Convallaria majalis, which is not native to the plains of Sharon. The Shoshana, Rose/Lily of Sharon, that is referred to in the Song of Solomon is not this plant, but an undetermined flower. As I noted in an archived discussion:
The actual identity of biblical plants is an ongoing (and sometimes hotly contested) debate. The current forerunners for the Rose of Sharon identity are:
Lilium candidum, the Casablanca or Madonna Lily (pictured in the florist link supplied by Pashute) This theory is supported by the research of Israeli botanist Michael Zohary.
Tulipa montana (altenately Tulipa wilsoniana) and/or Tulipa sharonensis, wild tulips that grow on the coastal plain of Sharon.
Narcissus odorus, Sweet-scented Narcissus/Jonquil
And there are several more contenders. Simply put: botanists, the Biblical translators weren't.