"I can't believe they would do this."
Mrs Haworth has just turned 90, and has been living in a resthome since December.
In an email dated January 24, Public Trust advisor Yvonne Collins told Mrs Purdy's mother: "With regard to selling of the property, I will let you know when it goes on the market ..."
Ms Collins also said that if the family wanted to collect any personal effects or photos to let the Public Trust know in writing and the request would be considered.
But as well as this message, the email - which was copied to another trust worker - contains another internal email which appears to have been attached accidentally.
It said: "Re the furniture and other stuff, unless they want lots of things, we should be selling everything. It is not gifted specifically in the will ... . They haven't had anything to do with her for some time as far as I know, so we need to be careful that they don't end up taking everything and we end up with a fight between family members and other potential [beneficiaries]."
Mrs Purdy said it was very hurtful to read that part of the email, and called it "nasty".
In February, Mrs Purdy's mother wrote to Ms Collins requesting "a few wall pictures and unsaleable items, e.g. kitchen/dining ware and bedroom linens".
But the family said the request was never answered and they were not told the house was on the market.
"It's our family home - our family heritage," Mrs Purdy said. "I don't know how we can be shut out, it's absolutely horrendous."
Mrs Howarth's two daughters and Mrs Purdy are trying to find the sale price and settlement date.
"We just want my grandfather's Navy medals, the photo albums and the Plunket books - we honestly don't mind about the money," Mrs Purdy said.
The family say that Mrs Haworth developed dementia in 2002, two years before the death of her husband, Roger.
In March 2010, the Public Trust was given enduring power of attorney over her affairs.
Included in the empowering document was a clause saying that Ms Collins, the witness, said she had "no reason to suspect the donor was or may have been mentally incapable at the time the power of attorney was signed".
Mrs Purdy called this "a joke" because her grandmother had obvious dementia.
Public Trust spokesman Brent Woodhead said Mrs Haworth had appointed the trust under an enduring power of attorney to act in her best interests.
On Monday, the family of Mrs Haworth had raised questions about the issue, , he said.
"We take matters like these very seriously and are now answering the questions with the family in the first instance and within the boundaries Mrs Haworth has set with the enduring power of attorney."
*This story has been corrected from the original article in the Herald's print edition this morning and from the original edition posted online. The earlier report stated that the property had been valued at almost $3m.