Mahendru started modelling at the age of 13. She was discovered by poet and lyricist Kaifi Azmi who recommended her to Basu Bhattacharya. Basu cast her in Uski Kahani in 1966. Uski Kahani was the debut film for Mahendru as well as the first directorial venture of Basu Bhattacharya. She later went on to act in films such as Jewel Thief, Bandhan, Dastak. She never made it as a leading lady and moved to character roles. She made a comeback in the 1990s in television acting in various soaps. She played Trishna's mother-in-law in the TV serial Hamari Betiyoon Ka Vivaah on Zee TV. She acted as Maan's daadi in Geet Hui Sabse Parayi. Currently, she is playing the role of Jeevika's, Maanvi's, and Daboo's daadi in Ek Hazaaron Mein Meri Behna Hai.