"We are very satisfied with the results. This election is proof of our solid unity in Pakatan Rakyat," she said.
Mariah also attributed DAP candidate Wong Ho Leng's historic win to the campaign machinery of the respective parties, echoing the view of DAP secretary general Lim Guan Eng.
She also said the win this time "is worth every effort", as it had taken place in a consitituency which had traditionally been exposed to only one side of an election campaign.
Mariah admitted that the initial feeling among party workers had not been optimistic.
"Looking at the (BN) flags hoisted around the houses, we thought we'd lose. It turns out that they just did not want to be seen as supportive of Pakatan Rakyat," she added.
Mariah also said rumblings among the Malay electorate against prime minister Najib Razak was a factor that contributed to BN's defeat.
She said Malays in districts such as Nangka, Pelawan and Seduan had been disappointed by Najib's 'biased' campaign visits, which had ignored the minority Melanau Malay community.
"It may be a protest vote against Najib," she said.