A BABY plunged 13 floors to her death yesterday after her mother tripped over a step at a Kwai Chung flat and lost hold of her. Leung Kwong Kwai-ying, 30, had taken Leung Chi-ching, who was nearly six weeks old, to her grandparents' home in Lok Yiu House, Lai Yiu Estate, for a family dinner to celebrate in advance of today's winter solstice. Shortly before 4.30 pm, as Mrs Leung walked to the balcony from the sitting room with Chi-ching in her arms, she tripped over a step and lost hold of her, propelling her out of an open window. Mrs Leung, who had travelled from her home in Wong Tai Sin, became hysterical and collapsed after the tragedy. She was in Princess Margaret Hospital last night.