Morissette's publicist told The Canadian Press that the photo tweeted Monday was actually taken on Oct. 10 at a private residence in L.A.
"She was indeed sick, which is why she unfortunately could not make the trip to Ottawa," said Morissette's publicist via email.
The $400 per ticket benefit was to raise money for Fertile Futures, an organization that connects cancer survivors with information and treatment so they can have children after beating their illness.
Morissette had been advertised since the summer as the marquee performer at the annual concert, with CBC personality Rick Mercer hosting for the sixth year in a row.
After booking Morissette in July, organizers were told Friday evening by her agent that the 40-year-old singer couldn't make it. Canadian rock legend Burton Cummings filled in instead.
On the evening of the event, Morissette posted pictures to Instagram and Twitter from a beach, mentioning the Adrienne Shelly Foundation, a New York-based charity that raises money for women filmmakers.
Several cabinet ministers and Liberal Leader Justin Trudeau attended the Monday night event. Some in Ottawa tweeted Morissette back.
Cummings charmed the crowd at the Great Canadian Theatre Company playing hits from the Guess Who and his solo career, sitting alone at a digital keyboard. At the end of the gig he saluted the work of Canadian servicemen and women, and then took pictures with fans.
The Hope Live event was launched by Rogers Communications executive Heidi Bonnell, herself a survivor of melanoma and non-Hodgkins lymphoma. Bonnell and her spouse had frozen embryos before her chemotherapy, and two years ago a surrogate gave birth to their twins.
She announced Monday that 300 men and women have so far been helped with fertility preservation through the money raised at the event.
"All's well that ends well. It was an exceptional evening that raised a large amount of money and was a huge amount of fun," said Bonnell, who pegs the amount raised at approximately $150,000.
"Burton Cummings really stepped up and gave it his all, and the audience loved it. It was a frustrating weekend, but an amazing event."
Meanwhile, Cummings documented his own response to the hurried weekend with a Facebook post.
"I'm the biggest Alanis fan you'll ever meet," he wrote. "I've championed her artistry for years. I was thrilled to meet her years ago at the Junos and have a beautiful photo taken of the two of us.
"It was a heavy charity event with power and wealth in full evidence, and it was all for good reasons," he added later in the post.
"Fascinating to be at the centre of the whole deal, especially in light of the fact that I was 'filling in' for Alanis."
Previous musical headliners included Jann Arden, Gord Downie, Randy Bachman and Serena Ryder.
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