Over-irrigation could be to blame.
Police are arming themselves in Canterbury from Friday as gang tensions increase.
She was charged with murder on Wednesday.
The 55-year-old is due to appear in the Christchurch District Court on Thursday.
"We believe this is an isolated incident."
The body was located on Wednesday morning.
Ngaire Ginders, 40, was last seen on December 29.
It aims to teach non-Muslim New Zealanders about Islam.
The holiday road toll is now more than double last year.