I have seen this numerous times and while I don't hate her character I don't get what's so award worthy about her performance. It just seems kind of meh to me. It also just feels pretty similar to what you would see in several TV shows. It's not horrible or anything. But it also doesn't make me go, "Wow! She was absolutely amazing and should win an award for it!"
shareI'm no expert on acting mind you, but I think so much of her performance was manifested in a beneath-the-surface manner, understated I think is the term. Another way to say it is that a lot is expressed and conveyed with a minimalist effort on her part.
That kind of performance may seem effortless, even lazy or "meh" as you put it, but it does take a great deal of talent.
I can't remember who she was up against the year she won but I'm such a fan of this film I'm going to go on the record and vote that it's not odd at all that she won.