Rachel, who has never had her hair cut short, said she was "pretty nervous, but looking forward to it at the same time".
"I have had a lot of support from friends, family and people I know or my family knows and a lot of girls from school. The teachers and students at school have been really supportive, too."
She has already doubled her goal of raising $1000, thanks in part to a video she made promoting her cause.
"I made a video which I put on YouTube and Facebook and after I put that up I got $1000 in one week," Rachel said.
New Zealand Breast Cancer Foundation fundraising development executive Fay Holahan had been supporting Rachel and would use the video as an example for other fundraisers.
"I asked if we can use it in the future if someone else is doing something similar and needs ideas," she said.
Mrs Holahan said Rachel's money would be used towards awareness campaigns, education and research grants.
The commitment of a 16-year-old was outstanding, she said.
"It's fantastic and we really appreciate it, not many people at the age of 16 are wanting to shave off their hair. We do get school groups and things that raise a couple of hundred dollars, but not really to this extent."
The shave would take place at Sacred Heart College before the end of the term.
Donate at www.nzbcf-fundraising.org.nz/rachelbird and watch Rachel's fundraising video at www.youtube.com/watch?v=SNzP9XG1lBY