When Devi Durga killed Demon king Mahishasur, she was offered a white lion that is symbol of strength, braveness and life.😊🙏 It may also show that the lion is a symbol of uncontrolled animalistic tendencies (such as anger, arrogance, selfishness, greed, jealousy, desire to harm others etc.) and Devi represent beauty and light having one softer side sitting on it reminds us to control these qualities, so that we are not controlled by them. Devi, mahamaya or kanya riding the lion symbolizes her mastery over all these qualities. This suggests to the devotee that one has to possess all these qualities to get over the demon of ego.