Not sure where lien came from(I thought it was the 'only mine" title she had received but it's not...), but I'm pretty sure he was calling MC that in the cliff not the other girl. I'm pretty sure he didn't even care enough to talk to her and just killed her.
Oh! Thank youuuu!! Now i know! 〜(꒪꒳꒪)〜
That's a translation issue. In the raws her fake name is spelled with what can be literally transated as "Riin", pronounced Ree-in (like green without the G). And it is spelled with the alphabet the Japanese use for foreign words(katakana). Since japanese does not have L sounds, they use the forgien-words R character instead (see: Luffy vs Ruffy)
The translator didnt read the other chapters and so didn't know how the previous groups had done it.
Wait why did he call her lien at the end? He also called the bitch girl lien (at the cliff) or im just tripping??