(Years later) After wondering the same for a long while I realised some of her expressions actually reminded me of Paris from Gilmore Girls. Might be just me.

I think she looks quite a lot like Renee O'Connor from Xena. Or at least, that's who I decided who she was reminding me of.
http://www.imdb.com/media/rm4146958848/nm0640488?ref_=nmmd_md_nxt

I thought I might have seen her on the Peep Show but it's not on her IMDB list :S

Dammit, yeah, you might be right- The girl down the well in Silence of the Lambs- Katherine Martin? Definitely dead ringers ( even without my looking her up ). Good work, mutteri!

I think I know why she looked so familiar. I was watching The Silence of the Lambs just now and I saw Brooke Smith (who also plays Dr. Erica Hahn in Grey's Anatomy) and then it clicked. I'm pretty sure I mixed Gemma Whelan with her.

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She was in Gulliver's travels (the jack5b4 black version) and the wolfman

I'm with you! She looks so familiar in GoT but I can't place her, and I haven't seen any of her projects listed on IMDb.
She slightly resembles Mayim Bialik from the Big Bang Theory, but I don't think that's who I'm thinking of.

She very subtly reminded me of Calamity Jane from Deadwood.

She looks very familiar to me also; I finally figured the resemblance is to Russell Crowe.

I just watched S1E2 of Call the Midwife, and I was sure that the pregnant teenager was played by Gemma Whelan. I was wrong, but they sure look alike.
Do you watch Call the Midwife? Maybe that's who you're thinking of.

I had the same experience when I saw her in GoT: Where the hell have I seen her before? It took some time until I realised that she reminds a lot of Mac from Veronica Mars. Not the same actor though.

I think she looks like Amy from Big Bang Theory.

Yes, Chloe Sevigny.
I am just now watching GOT. I have some catching up to do.

http://www.imdb.com/board/20001721/
Chlo Sevigny maybe?

Ha, I was watching 'The others' the other night, and the daughter (Alakina Mann) looked like her but younger.

Glad it's not just me. Anyone come up with anything, let me know!

I have the same problem after watching a few episodes of the 2nd season of GoT. I think the face I'm thinking about is not actually Gemma Whelan but someone with a resemblance to hers in the role of Yara. Maybe a bit older with a lower voice I've searched for hours, can't find anything. I'm positive I've seen her or her lookalike (I have a habit of mixing up actors, like Christopher Walken and Jon Voight) somewhere. But I'm not even sure if I'm thinking of American TV shows or what.

Just saw her in this http://www.youtube.com/watch?v=XfONJQ7DudQ
you're adopted