Lovely imagery! I get the idea that by 'drifty' the writer (surely a lady?) means that sort of floaty vagueness of someone who is happy but a bit distant; a bit 'dreamy' — as I guess one might be if one were pregnant.

And I hope she means overwhelemed at the joyful prospect of motherhood, hence my suggestion of 'comblée' — I can just picture exactly the sort of look described!

Note that the 'all' refers to the 'look'; it's often associated with a look, like someone going all misty-eyed. I haven't seen an equivalent construction used in FR, though I have of course seen 'tout' used in a similar way.

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Note added at 10 mins (2013-03-13 20:57:04 GMT)
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In the light of your previous question, I can't help thinking that it is indeed the woman who fancied the guy, and so puts on her best 'expectant mum' act to try and hide it.