It's possible it could be:
* A variation of the Irish name "Sheáin," meaning "God is gracious."
* A combination of the names "Sharon" and "Anne," drawing from their respective meanings (meaning "plain" and "grace" respectively).
* A completely original name created by its parents.
Ultimately, the meaning of "Shyanne" is open to interpretation. Many parents choose names based on their sound, appearance, or personal significance.