BELLE - KNUDSEN - ELLINGSDATTER

I have Marthe Rognaldsdatter BELLE (b. abt 1793) married to Knud SIMONSEN 12 Nov 1823, Aurland. Where did the BELLE surname come from? Her parents, Rognald KNUDSEN (b. abt 8 Mar 1760)/Anna ELLINGSDATTER (b. abt 1758): I also know that Rognald was a twin of Luchriis. No surname for Anna? When/where were they married? Thank you for any information in this line. [:I] Luella