Photographs of 20-year-old Sam, whose last name has been omitted to protect her privacy, are being circulated on anonymous online forum 4chan.
Users of the website posted her photo, which was originally taken from Reddit, and falsely claimed that she was the gunman who opened fire on Robb Elementary School in Ulvade, Texas in a murderous rampage this week.
The shooter, identified as Salvador Ramos (18), was killed at the scene by police.
And Republican Representative Paul Gosar, of Arizona, spread the rumour by taking to Twitter and writing that the gunman was a “transsexual leftist illegal alien named Salvatore Ramos.”
Gosar’s tweet has since been removed from the platform but photos are Sam are continuing to be shared online.
“This isn't the first time I was harassed, but it is the first time I've been accused of murder,” Sam told NBC News on Wednesday.
However, she said she feels annoyed about the mix-up more than anything and urged people to be careful about what they read online.
“I’m more worried about the families of the victims of the attack.
“Transphobic people exist and people are quick to blame someone for terrible things instead of looking for the truth about what actually happened.”
In an effort to debunk the conspiracy theory, Sam shared a photo of herself on Reddit in front of a transgender flag, writing: “it's not me, I don't even live in Texas.”
She said that trolls “just took my photos and used it to spread misinformation” before adding: “I don't want fame, I just want to live without being attacked when I leave my house.”
Meanwhile, Ramos’ mother Adriana Reyes admitted she was “surprised” her son was behind the horrific massacre because “wasn't a violent person.”
She acknowledged that son was a loner who “kept to himself and didn't have many friends” but rejected claims that she did not have a good relationship with him.
Reyes told the Daily Mail: “My son wasn't a violent person. I'm surprised by what he did.
“I pray for those families. I'm praying for all of those innocent children, yes I am. They [the children] had no part in this.”
She added about her son: “I had a good relationship with him. He kept to himself; he didn't have many friends.”