"I didn't pay attention when I was getting it, so I just got it and ate it," she said.
Diamond Brooks father told WSB-TV's Matt Johnson that an ambulance brought her to a hospital where doctors told them she had marijuana in her system.
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Brooks and her family claim the marijuana came from the cookie.
"If she told me what was in it, I never would have got it from her," Brooks said.
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The DeKalb County School District sent the following statement:
"The student ingested a dessert, but it cannot confirm if it was laced with a drug. Our investigation will shed more light on what occurred."
While the district investigates, Diamond Brooks' family said she will be at home because the district suspended her.
"She didn't know what it was. She didn't intentionally do no drugs," Gary Brooks said.
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Gary Brooks showed Johnson the paperwork doctors gave him when they treated Diamond for confusion on Friday morning.
He said he remembers watching her throw up from her hospital bed.
"If something happened to her, I would have lost it," said Gary Brooks.
Now, he said he loses his temper when thinks about how he has to fight to get his daughter's suspension overturned.
"When you spike somebody's drink, they don't know, so they are supposed to get punished for what happened? That don't make sense," Gary Brooks said.