This new siren is probably Emily Swan. Her echo logs are in the BL presequel. She is an artificial siren created by the Guardian. That is why her tattoos are pink. Highly likely this is her.

So, I've researched this quite a bit and I think this new BL4 siren is Emily Swan. The echo logs in the BL presequel speak of an artificial siren created by the Gaurdian. As Emily was about to die as a child in the hospital, the Guardian came to her and emitted a "pink" light saving her life. Artificial Sirens have different colors, but the Sirens who are chosen by the universe are light blue. Troy was red because he was coned to Tyrene as a fetus and was not the female chosen by the powers that be. Emily was endowed her powers by the eridians who seem to be led by the Timekeeper. I believe this Timekeeper sent the Gaurdian to save Emily because he knew she would be a badass in the great war that was foretold on the hidden planet Kairos. This war will hopefully be the reason all our Sirens return not from the dead, but because the Timekeeper pulled them from their impending death nano seconds before they actually died. Look up Emily Swan and you will see this.