A distraught Ms Sim Yee Ling, whose 15-year-old daughter Ng Yuk Tim was murdered, said she was crushed when she read some comments online.
Yuk Tim was killed on Monday and stuffed in a suitcase that was dumped in Shah Alam, the state capital of Selangor. Her body was found on Tuesday.
A 23-year-old suspect whom she had met to discuss cosplay costumes has been arrested.
Said Ms Sim, 35: "The things that people have been saying online about my daughter are horrible."
"Some are saying she deserved it because she went to see a guy on her own. My daughter had always been a good girl."
She also wrote a heartfelt post on her Facebook page on Wednesday.
She said her daughter was such a caring person that she would advise her and other family members to be careful and drive safely, The Star reported.
"I always felt that her caring reminders were annoying at the time," the mother wrote.
She said her daughter was a very simple girl who was not interested in dressing up or wearing make-up.
Wrote Ms Sim: "I always felt that her skirt was too long and her hair too short.
"She always went out wearing double shirts and long pants. I always felt she doesn't like to wear make-up. When I go out, she is at home and reminds me to 'be careful, be careful!'