Did Yuru's mother really fall off a cliff?

Really. According to the story of Chang Feng Du, her mother unfortunately fell off a cliff on the way to escape and was rescued when she fell off the cliff. Then, she hid in the countryside of Yizhou until Liu Yuru ventured to buy goods in Yizhou and met Su Wan again. So he was taken back to Youzhou, where his mother and daughter reunited and lived with Jiang Rou. Life is dull and happy.