Skye is shown cutting herself with a razor blade in a prominent spot on her arm, then in her next scene she's wearing a sleeveless outfit and has no injuries or scars.
When the girl notices the pool of blood on the grate, the officer identifies it as human blood. There's no way for him to know this at a glance. Human and animal blood is virtually identical to the naked eye.
Noelle makes absolutely no effort to cover her tracks when she commits the murders. Her DNA would have been left everywhere, and she would be quickly identified.
If Noelle's DNA was never in the system, including voluntary ancestry sites, she would have remained a Jane Doe until the police had something to test it against.
Noelle's neighbor tells her she used to go by Daisy until "something happened" that caused her to change her name to Skye. When Noelle is viewing the report for the incident that happened to Skye, it shows her name as Skye. When the incident occurred, she was still going by Daisy.
Both names appear in the police report. The file could have also been updated at a later date.