The 49-year-old woman, who cannot be named to protect the identity of her daughter, was informed of the Crown's decision last month. She said she was told the charges are being dropped because the case had taken too long to get to court.
"This is crazy," she said in an interview with The Canadian Press.
"The Crown said to us this happens all the time. Well, it shouldn't. This shouldn't happen to anybody.
"If there's a problem with the courts not having room in them or not enough Crown prosecutors it should be changed."
A spokesman with Alberta Justice said he wasn't immediately able to comment on the case. Rob Anderson, the Opposition Wildrose member of the provincial legislature in the mother's constituency, detailed the case during a heated question period Thursday.
The young woman, who is now 27, was allegedly sexually assaulted by a person in a position of trust from age nine until she was 17. She came forward six years later and charges were laid in September 2009.
Although a trial date was scheduled for this month after a series of delays, the Crown told the family he wouldn't be opposing a defence motion to drop the charges, the mother said.
"He called us back and said, 'I'm not even going to fight this because they're right. It has gone on too long and they have a case.' So, they threw it out in October."
Anderson told the legislature the sexual assault charges were thrown out due to a shortage of Crown prosecutors.
"I want to know what kind of pathetic excuse for a justice system charges an individual for violating an innocent girl for eight years and then denies that victim her day in court?" he asked Premier Alison Redford.
Redford said the government would review the case.
"I do not actually believe this is an appropriate question to be raised in such a political manner. We have said we will look into the facts of this case and we will provide a fulsome response," Redford replied.
Anderson demanded the Alberta government launch a public inquiry into the case. His questions led to a testy exchange with the Speaker Gene Zwozdesky, who chastised Anderson for continuing to ask questions on the issue after the premier's answer.
"These questions are entirely appropriate and you'd better start thinking about the girl instead of your political skin. I want accountability on this," Anderson said. "This girl is a citizen of Alberta and is one of the most innocent victims and deserved better than this."
The mother said the family would be happy to meet with Redford or the province's justice minister.
The effects of the case on her daughter have been devastating.
"She was very angry. She wanted to go out and help other people and tell them the right thing to do is to go to court and charge these people, don't let them get away with it, and now what can she tell them?" she said.
"She's devastated. What does she do now?"
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