30Rock?

I've been watching the last few episodes of Season 3 of 30Rock. In the last episode of the season a charity song is performed by a number of celebrities. In the back the group singing along with someone I didn't recognise (probably is famous though) I'm sure I saw Amanda Abbington.

I checked the cast credits but she was not listed but then she did not actually speak, she just mimed to the song.

So I'm wondering if anyone else has seen the episode and saw Amanda or was it just my imagination?