This has two meaning for me. I find both Nala and Sarabi beautiful, but Sarabi has both outer and inner beauty and is very underrated as far as a character goes. First of all, she looses everything including her husband/mate, son, and kingdom all in one day. She has Scar take over the Pridelands and hyenas, yet, in spite of it all she stays proud, regal, and determined. She also stays loyal to the memory of Mufasa even after Scar physically hurts her for doing so. She still is proud and loves Simba for coming home and taking the throne and supports Nala as the new queen. She is just a great character and strong. She is also the second to attack Scar after Nala and realizes the lies Scar fed her son to make him feel responsible for his father's death.
Nala is also beautiful both inside and out. First of all, she essentially grows up in the lion version of a concentration camp but still has a positive, strong, loving personality. She resists Scar's attempts to make her queen and leaves to find help. She tells Simba his duty is to his kingdom and his pride even when Simba doesn't want to face the facts. She could have been bitter towards Simba for living and not coming home, but instead she wants to make things right and restore order to the kingdom. She wants to take her place as his side as queen.