Well,
Conways, All the Worlds Fighting Ships 1922 - 1946, makes no mention of any significant change in the Fletcher class DD other than the bridge, and weaponry variations.
The La Vallette is given no special mention.
So other than, the La Vallette, being the third or fourth keel laid for the Fletcher class at the Federal, Kearny ship yards, I see no reason for the class designation discrepancy other than the cruise book author's memory of ships of the class.