After a group meeting on Thursday afternoon, Ruohonen-Lerner told Yle that the posting was harmful to the party and its parliamentary delegation.
She said that this kind of comment is unacceptable under any circumstances.
"The discussion was lively," said Ruohonen-Lerner.
She said she did not accept Hirvisaari's rationale that the posting was meant as humour.
"It's bad humour. It does not suit our parliamentary delegation or our party," she added.
Ruohonen-Lerner said she now expects Hirvisaari to do as the party has proposed.
"Of course we expect Hirvisaari to take this seriously," she said.
Aide could be out fast
Ruohonen-Lerner noted that since Eronen began work less than three months ago, she is still under a trial period and can be dismissed quickly.
In October Finns Party MP Teuvo Hakkarainen said in an interview that immigrants and homosexuals should be banished to the island province of Åland.
Last summer Finns Party MP Jussi Halla-aho raised ire by suggesting that a return to military dictatorship would be the only way to solve Greece's problems. He, too, argued that the comment was meant as a joke.
Both Halla-aho and Hirvisaari have been convicted of hate speech for earlier online comments.
The Finns Party earned the third-largest number of seats in last spring's parliamentary elections, leaping from five seats to 39. Since then, their popularity has been sliding in public opinion polls.
