She joined the party here in the presence of senior BJP leaders Ravi Shankar Prasad, Kailash Vijayvargiya and Mukul Roy.
"There is no democracy in West Bengal. 'Crimocracy' and 'thugocracy' have replaced it," Ghosh told reporters.
Vijayvargiya said her joining the BJP will strengthen the party.
Sources said Ghosh was once considered close to the state's ruling dispensation but had a fallout later, adding that a case was also registered against her.