I wouldn't be surprised if her sister hired the pandit to tell Tara that she can't have kids. At this day and age, for a family as rich as theirs, the first thing a normal person would do is to go see a gynecologist and get a complete checkup. She has to have more options than a surrogate mother. I can't believe the show at times.
A surrogate mother would carry a child that would be genetically Tara and Brijesh.