I think the girl Rhue is looking for is the girl with purple mask that got it burnt. There is lots of evidence that its her.

I forgot her name sorry for any confusion.
For example:
Here was a part of there conversation under the volcano well not exactly, but similar. Rhue says,"I would do anything to find her". Girl with mask asks,"Even if her face was burnt and she was ugly?". Rhue replies,"Yes no one can replace her!". Well maybe that was too much like a soap opera.

Anyway she did tell Dancing Violet that she couldn't be the girl because she knew her. Also about the face burnt part, it's in Rhue's little day dreamy blackout things. From evidence in Episode 5 it showed that Slade is 100% the girl with the burnt masks brother. It's kinda ovious because she says "wat about your sister?". Then it showed Rhue day dreaming about a guy, his sister and mother. Then the mother burnt her face just like wat happened to the girl with the mask.
What do you guys think? Please reply with your thoughts.