She looks like some kind of wild, feral elf but she's shorter than a human or elf. I know Terrinoth races are not specified anywhere, but does anyone have a clue? 

I'm with you, in that I think she's a feral elf.  Until FFG comes out and says otherwise, that's what I'll continue going with.

I just had another thought.  I was looking through my 1e monster cards a little while ago and it came to me.  Could Ashrian be a Deep Elf?  Given the similarities in garb and markings…also it is stated in her flavour text that she has no memory of who she really is or where she came from, so perhaps it could be possible she was once among the minions of the Overlord.  Maybe cast-out, left for dead, something along those lines.

As I said, just a thought.

 Sounds like a good allegation to me. I'll allow it! lol 

She doesn't look like a deep elf to me.  She looks like a regular elf who's just shorter than average.  That's my personal opinion, anyway.

FFG has been known to mix things up with regard to standard sci-fi/fantasy tropes in the past (like giving two of the leaders in TI3 the same name to remind us that multiple people with the same name can exist.)  IMHO, this is just them reminding us that not every member of a given race is within a couple inches of the same height.