Who is the girl in the distress call Ian receives in Last Seen?

Here’s how the plot confirms this identity:

• Sarah (played by Chloe Jean Lourdes) calls emergency services (“000”) saying she might be “Mags” (Ian’s nickname for Maggie). Ian answers. - In Episode 4, Jenna Reid admits publicly that Sarah is not her and Henry Reid’s biological daughter—confirming that Sarah has been raised under a false identity. - It is confirmed Sarah is Maggie Ridley; she grew up believing she was Sarah Reid, named after Henry and Jenna’s deceased daughter, and was raised by them under that identity.

So the girl in the call turns out to be Ian’s missing daughter.