Please Help Me Translate This Sentence

Hi anyone and everyone !
I'm hoping someone can help me translate this. I know what the words say, I just don't understand the grammar. What exactly is this trying to say ?

sono hito wa, yukue shirezu no rinne no haha

Is it somehow saying that that person IS Rinne's mom ? I don't understand the part saying "without revealing/discovering the location of"

I attached a photo of the text's origin. (it's purple, in the middle)
Thanks so much !

行方知れずの means "missing".

死神乙女…
その人は、行方知れずのりんねの母親
Shinigami-otome,
she is Rinne's missing mother.

Toritoribe said:

行方知れずの means "missing".

死神乙女…
その人は、行方知れずのりんねの母親
Shinigami-otome,
she is Rinne's missing mother.

Click to expand...

OH ! It means missing !!! Thank you so much ! <3