Her planned ski trip to Japan has clashed with Otago's surprise appearance in the final and the Sparks will have to make do without her skills.
Nielsen has been a key performer for Otago since transferring south from Northern Districts three seasons ago. But she has struggled to make an impact this summer and has not bowled a lot for Otago in the campaign.
She played for the Melbourne Stars in the Women's Big Bash League (WBBL) in Australia and is due a break from the game, Sparks coach Warren Lees said.
''It is something she planned a long time ago and it has something to do with how tired she is with her commitments over the last three years,'' he said.
Otago has otherwise named an unchanged line-up for the final, which will either be at Hagley Oval in Christchurch or Mainpower Oval in Rangiora.
The team will travel to Christchurch on Friday and train later that day.
Sparks captain Suzie Bates is spending the week in Auckland and will link up with the team on Friday.
She has not been as instrumental with the bat as she has in previous years and missed a game to play in the WBBL. But she is a class performer and it would be just like her to play a starring role in the final.
Katey Martin is Otago's leading scorer in the competition with 116 runs at an average of 38.66. She is enjoying a fine patch of form and will be a prized wicket for Canterbury.
All-rounder Leigh Kasperek completes a trio of dangerous players for Otago. The off-spinner is the joint leading wicket-taker in the tournament with six wickets at 16.50.
Lees said the team would lean on those players again but it has developed more depth this season with the rise of players such as Caitlin Blakely, Victoria Holden and Millie Cowan which has helped get Otago through. Import Beth Langston has been a good acquisition as well.
