Nadia is a stage name while Sadeena is her real name. She has ties to the villageand consides herselfa big sister to all the village kids, especially Raphtalia. She was almost alwaysin her beastman form which is why Raphtalia didn't recognize before the fight
When I first saw Sadeena's "animal" form it looks so cute and squishy, I was kind of surprised to see her human form. I didn't follow the main series, I'm just here for food.