That, actually isn't that bizarre (at least compared to most Henry things... Maybe I'm just not grasping the bizarreness of this cause I haven't seen this 'smile' myself).

A lot of people (Me included) can't force fake smiles, it requires the actual feeling to be there.
Henry's just sounds like a more extreme version of one with a bad fake smile. Maybe she's trying too hard?
Maybe that's just how her personality compensates for a smile when the natural happiness isn't there?