"The war crimes need to be investigated; the crimes against humanity clearly continue, the evidence is very strong," Rhiannon told reporters at Sydney Airport on Monday after arriving from Colombo after a four-day fact-finding tour.
She said the Australian delegation to Colombo "should not be headed by Mr. Abbott as prime minister. Surely they should take a leaf from the Canadians," Rhiannon said.
Abbott rejected the demand to snub the meeting, saying he wanted to maintain "the best possible relations" with Sri Lanka, which readily takes back asylum seekers who attempt to reach Australia by boat.
India announced Sunday that Prime Minister Manmohan Singh will be the second leader after Canadian Prime Minister Stephen Harper to boycott the Nov. 15-17 meeting. There are 54 members of the Commonwealth, a loose association of former British colonies.
Abbott won elections in September on a promise to stop asylum seekers reaching Australia by boat.
"I am not inclined to go overseas and give other countries lectures," Abbott told Sydney radio 2GB when asked about allegations of Sri Lankan human rights abuses.
"I don't say everything's perfect there for a second, but I think things are getting better and while yes, I will be urging the Sri Lankan government to respect everyone's rights, I think I will also be acknowledging that a lot of progress has been made," he said.
Human rights group Amnesty International said the detention of Rhiannon confirmed a pattern of continuing human rights abuses in Sri Lanka.
The decisions by the Indian and Canadian leaders to not attend the summit is expected to sharpen the focus on demands by Western nations and rights activists that Sri Lanka account for thousands of civilians who are suspected to have died in the final months of a quarter-century civil war that that ended in 2009 when government forces crushed separatist Tamil rebels.
The APNZ news service reported that the New Zealand lawmaker, Jan Logie, said she was safe after her detention.