Kim Leadbeater said the former Batley and Spen MP, who was elected at the 2015 general election, was “over the moon” to have won the vote to serve the area she grew up in.
“Jo’s life and her career were cruelly cut short just over a year later.
“I recently celebrated my 42nd birthday and it was tough because Jo, my older sister, never got to see 42,” Ms Leadbeater added.
“What has helped get us through as a family is the amazing way that so many people all over the country have joined with us in keeping her memory and the values she stood for alive.”
Millions of people took part in get-togethers on the anniversary of her June 16 murder, Ms Leadbeater said, with another weekend of events planned on June 22-24 this year to coincide with what would have been Mrs Cox’s 44th birthday.
Ms Leadbeater added: “Most of all, I just want to say thank you to everybody who has got behind our efforts to build stronger communities and heal some of the divisions in society.
“Jo believed passionately that no problem was too difficult to overcome.
“I owe it to her to be guided by that in the months and years ahead.”
For more information about next month’s events, which aim to bring communities together, visit the website at www.greatgettogether.org.