Well I watch a lot of TV - like, a LOT - so I like to think I can distinguish bad acting from good. I do like her character from the books (she's not one of my favourites though), but her performance was quite stale. Sometimes when she spoke at the dinner, it felt forced and it actually made me picture the scene being produced. But I have to say her scene at the orphanage was quite touching and natural. Possibly the dinner was filmed first and it was just a case of nerves or getting into the swing of things?
I'm not sure you needed the tags btw, but it's always better to be safe than sorry!