While she has actually sung a few of her mother's songs the reason why Liza probably does so sparingly is because she's a star in her own right. When she was a teenager she made a definitve break from her family legacy -- insisting that she be introduced as Liza Minnelli, not "Judy's daughter" and living exclusively off the money she earned, never taking another cent from her mom. On the other hand, Judy's other daughter, Lorna Luft has an entire CD dedicatefd to her mother's songs and its great. Liza has no need -- her string of hits range from New York, New York, to Liza With a Z, Cabaret and Maybe This Time to But the World Goes 'Round. I saw in the comments too a mention of her being "too drunk to remember the words". Not that she needs defending but while it's easy to discount her, she gave up drinking years ago. And, after all she's been through (ranging from personal/family tragedy to a near-fatal disease where they told her she would never speak again) she remains one of the most talented performers of the 20th century. Alcoholism is a disease, one that has leveled many entertainers, but is just another hurdle not strong enough to overcome the star power of Liza Minnelli.