They are accused of offering advice on trading high-risk foreign currency derivatives over the social media platform
"We arrested the second person, a woman named Shashi Singh, in our ongoing investigations of the case on Saturday," R.K Gaur, a CBI spokesman, told AFP on Sunday.
Sengar appeared in court the same day and was ordered detained for seven days.
The girl's family - who fought unsuccessfully for nearly a year to get police to register their case - said Singh had taken their daughter to the state legislator on the pretext of a job.
Singh then allegedly stood guard at the door while Sengar raped the girl, the family's initial complaint to police stated.
Details of the rape and murder of an eight-year-old girl in Jammu and Kashmir state also made national headlines.
The girl was kidnapped, drugged and repeatedly raped over five days - including inside a Hindu temple - before being strangled and beaten with a rock.
The killing in the city of Kathua has heightened communal tensions in India's only Muslim-majority state.
Scenes last week of Hindu lawyers trying to stop police from entering court to file charges against the eight accused - all Hindus - sparked nationwide revulsion.
Two state ministers from Modi's BJP resigned for attending a rally by local Hindu groups in defence of the accused.
The protesters called for a fresh investigation into the case, alleging the real culprits are still at large.
The crimes have shaken India in a way reminiscent of the fatal gang-rape of a Delhi student on a bus in 2012 that made headlines around the world.
Modi on Friday promised justice for the victims as anger mounted, while India's women's minister called for the death penalty for child rapists.
They are accused of offering advice on trading high-risk foreign currency derivatives over the social media platform
The two days of hearings at the International Court of Justice are part of a case brought by South Africa accusing Israel of genocide
Chennai Super Kings, who are fourth, and Royal Challengers Bengaluru lead the hunt for the remaining playoff spot
The 22-year-old batter became only the fifth uncapped player in IPL history to score over 500 runs in a season
Brent had touched an intra-day low of $81.05 on Wednesday
Digital payments remain a rapidly growing sector
Imports of aid through southern Gaza completely halted as fresh fighting adds to distribution challenges
The Spice Board of India has taken steps to ensure the safety and quality of Indian spice exports to these regions