She is only choreographing Delhi Belly because Aamir asked her to. She only choreographs for her friends, her husband Shirish Kunder and her brother Sajid Khan she said. Delhi Belly is a sex comedy, which has Aamir"s nephew Imran Khan in it.
Aamir specifically wanted Farah to choreograph nephew Imran"s song because he wanted her to recreate the same magic she did years back in his movie Jo Jeeta Wohi Sikandar"s mega hit song “Pehla Nasha". In case you did not know, 'Pehla Nasha' was Farah"s first ever choreography and since then, she has worked only twice with Aamir, once in Sarfarosh and once in Dil Chahta Hai.