Who is Saeeda Bai from A Suitable Boy: A Novel and what is their importance?

Saeeda Bai is a notorious courtesan renowned for her singing. She is hired for private parties as an entertainer with some musicians who accompany her. However, that is not the way she makes most of her living. One man in particular, the Raja of Marh, is a frequent guest in her house who pays for her sexual services.