Curious to know why you didn't mention the designation of the Raja Beta here. And what makes you think the son is a good for nothing? And since she is an old lady she is most likely wired in a way that she considers her son to be her biggest asset. And it is the son who will most likely take care of her, provide, and protect till she dies. Even if the daughter wishes to, she may or may not be allowed by her husband or in-laws. So, it's still a gamble.
Indian parents in general are selfish creatures. They bring a life into this world purely with the intention of having someone who will take care of them when they are old, or to carry forward the family wealth. Now if she demeans her son at every given opportunity the fragile male ego can probably even kick her out of the house someday or stop caring for her since she will become a burden because she anyway doesn't respect his efforts. Would she risk it? I doubt.