Sasikala was introduced to Jayalalithaa by the IAS officer-turned-politician, VS Chandralekha. VS Chandralekha was the one who hired Sasikala's husband, R Natarajan as her PRO.
The relationship between the former Chief Minister of Tamil Nadu Jayalalithaa and Sasikala started off on a good note for sure but it did not end well. On Jayalalithaa's 69th birth anniversary, you should know how the relationship between Amma and Sasikala went sour over the years.

IAS officer-turned-politician, VS Chandralekha, had introduced Sasikala Natarajan to Jayalalithaa. Post that, their relationship has been pretty well-documented in Tamil Nadu politics. Over the years Sasikala became her confidante and moved into Jayalalithaa's house in Chennai along with her family.
In 1996, Sasikala was arrested by the DMK government for violating Foreign Exchange Violation Act and Jayalalithaa had distanced herself from the former for a few months. But it took very little time for Sasikala to regain Amma's confidence back again.
The relationship was affected by the Tansi Land deal in which Jayalaithaa was acquitted by the Supreme Court in 2003. Jayalalithaa had even expelled Sasikala and 12 relatives from the AIADMK party and also from her house in December 2011.
Check this video to know how the relationship between Jayalalithaa and Sasikala went sour:

