Whoa, she changed a lot. I didn't recognize her either, but a reverse image search worked for me.

EDIT: I think I misinterpreted your title; I thought you were looking for answers, but I think you just meant she looks very different. I'll push my answer down to avoid spoilers...

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Jewel Staite. Kaylee from Firefly. Jennifer Keller, Stargate: Atlantis.

Here's a gallery.

In my opinion she looked much better with a rounder face: 1, 2, 3.