Tilly Anderson, 10, was at the beach in Colwyn Bay when she was stung - sending her into anaphylactic shock.
Her father, Tim, tried to peel the trailing tentacles from her leg as her mother, Michelle, phoned an ambulance.
Paramedics gave the girl drugs after her leg began to swell before taking her to Ysbyty Glan Clwyd, Bodelwyddan.
Mrs Anderson, 30, said: "When he pulled her out there was a jellyfish with loads of tentacles wrapped around the top of her legs.
"It was horrible. Tilly was screaming out in pain as Tim peeled the main part of the jellyfish off and tried to unravel the tentacles."
She added: "My daughter's legs were swelling up before my eyes and she was going into shock. She was blistering and shaking from the pain.
"They were wrapped around her so tightly that we had to put her back in the water to peel them off.
"It was terrible, it looked like her legs had been burnt."
Tilly was playing with her seven siblings and parents on the beach at Colwyn Bay on Saturday, 8 August when she was stung.
Mrs Anderson said: "If the tentacles had been around her for much longer she would have been scarred for life.
"That night, she was at home in agony and barely slept. She's a lot better now, but she's adamant she won't be going into the sea again because she's terrified."
A Welsh Ambulance Service spokeswoman said: "We'd like to send our very best wishes to this brave little girl, and hope she makes a speedy recovery."
A girl from Conwy county was left "terrified" after a jellyfish wrapped 30 tentacles around her and stung her leg.