She had been prescribed with six scoops of Ensure, an oral nutrition supplement, to be taken three times a day.
During her time at the rest home, some nursing staff were confused by the woman's prescription, and on occasion only administered one scoop of the product instead of the prescribed one dose - which was six scoops.
Wall said the weight loss should have triggered multiple follow-up actions, such as a referral to a nutritionist.
However, timely action and appropriate follow-up did not occur while the woman was at the care home.
Colwyn House owner Heritage Lifecare chief executive Norah Barlow said there is no tolerance of any failure by staff to provide adequate care, nor their failure to show respect and empathy.
"It is unacceptable to have inconsistencies in prescribing of nutritional supplements as has been identified in the case," she said.
Barlow said Heritage Lifecare deeply regrets the inadequacies in care of a resident at the Hastings care home.
"We acknowledge that this follows an earlier, but unrelated complaint around the care of a resident at Colwyn, which was released last month," she said.
Barlow said they have apologised in writing to the families of both residents and spoken to them to answer concerns.
The report was critical of multiple failures by the rest home:
These included: not ensuring a complete care plan was prepared to guide staff when the woman first arrived; failure of multiple staff to administer the woman's Ensure in accordance with her prescription; and failure of staff to seek clarification of the prescription in a timely manner and to act on evident weight loss.
Deputy commissioner Wall recommended the rest home operator provide training to all nursing staff.
Teaching them on care planning requirements, monitoring and managing residents' nutritional needs, administering medication and the professional responsibility of nursing staff to question ambiguities and raise concerns.
Wall also said the number of staff involved in the inadequate care suggested a lack of understanding of the rest home's expectations, "a lack of critical thinking and a lack of oversight by the rest home".
Barlow said all of HDC's recommendations have been implemented at Colwyn House and they have employed a new management team.
She said they are undertaking an internal investigation and appointing an external auditor to review and improve training processes and culture.
"Heritage does not consider these historical incidents to be reflective of the standard of care or culture at the facility or across the broader network," Barlow added.