Okay, so here's what we know about Glimmer:

1. She's a Flasher

2. She's got long black hair

3. .....that's it

Wow, what a wellspring of information!!

I'm almost tempted to say that Quan and Mai had triplets, but I don't think that's logical, since Glimmer would have to live SOMEWHERE until she could join the Neverseen, but then again, we literally know nothing about her. Tam knows her backstory and why she joined the Neverseen, which means that it couldn't be something bad or else he wouldn't trust her as much as he does. And she's a Flasher.....

Honestly, as far-fetched as it is, her being a triplet fits. She could've been raised by the Neverseen or someone in it, which is why Gisela believes she's so loyal to the cause, and she's a Flasher, which kinda fits with a Shade and a Hydrokinetic. Plus, Tam says she reminds him of his sister, someone he trusts with his life, so it makes sense why he would trust Glimmer as well.

But I don't think she is, since there's a lot of logistical problems with that. And given we know nothing about her, it's really hard to say...

Let me know your guys's theories I guess, this was pretty much a useless chapter XD