Violet MacDonald, 74, has since died.
"The system has failed this resident and we will do our best to find out why," Fred Horne told the legislature during question period Monday.
"This sort of situation is unacceptable in this province in any circumstance. I have asked Alberta Health Services' on-site team to monitor operations at this facility until my questions are answered."
MacDonald was a resident for years at Calgary's McKenzie Towne Care Centre.
Her daughter, Cassie Liska, with the assistance of the opposition Wildrose party, held a news conference earlier Monday.
Liska told reporters that care home staff misled her on the severity of the bed sores on her mother, who suffered from dementia.
In February, MacDonald was left in a soiled diaper for two days, infecting the bed sores and causing severe blood poisoning.
Liska said even when staff were taking Violet to the hospital, they refused to let her see the extent of the wounds and even barred the door to her mother's room with a chair to keep the family out.
"I am afraid for not only myself, but scared for anyone who has a loved one that they're not able to be with 24/7," said Liska.
"Violet deserved better, and we deserved better.
"I'm here to tell her story today with the hope that changes can be made so nobody ever has to endure the abuse that my mother did."
Pictures handed out to media show MacDonald's buttocks were black from decayed flesh.
MacDonald was in and out of hospital for much of the rest of this year and died in late October.
Liska said the government only investigated the case after she insisted. A followup report ordered the centre to overhaul its wound dressing procedures and report back by the end of the year.
Wildrose seniors issues critic Kerry Towle said the case is further proof that the province needs an independent seniors advocate who can research these issues and not be beholden to the province.
"We would not accept children to receive this type of treatment under provincial care. Why would we allow the same thing to happen to Alberta seniors?" said Towle.
"It is why we made the child and youth advocate independent, and it's why we need to make the seniors' advocate independent.
"We need an advocate that can fully audit the system and identify the shortfalls."
Premier Alison Redford's government is bringing in a seniors advocate early next year, but the advocate will report to Horne and not the legislature.
NDP critic David Eggen said as long as the government continues to out-source seniors care to private providers, the problem will worsen — whether a seniors advocate is independent or not.
"As we lose control of the whole industry to privatization, then something like the advocate becomes less relevant," said Eggen.
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