With the game being the last opportunity for players to perform in front of the U19 selectors before the squad to tour America is selected, the Welsh side notched further scores through winger Becca Stilwell and outside half Stacey Saunders.
Llandaff North fought back as their experience allowed them to dominate posession in the last quarter and centre Jess Kidley broke through for what proved to be the decisive score.
The Wales U19 squad to go to Miami in February will be posted on theis website on wednesday.
