Barbara Zimmerman brought up a recurring question in connection with our recent Good Word mortify:
“Is it not more properly said: ‘Maud Lynn Dresser was positively mortified when she saw Portia Carr wearing the same dress as she at the spring cotillion?’ I say that because the full version of the partially unspoken clause is ‘as she was wearing’? You wouldn’t say ‘Maud Lynn Dresser was positively mortified when she saw Portia Carr wearing the same dress as her was wearing at the spring cotillion.’ Or at least I think you would not.”
Barbara is right, of course, I wouldn’t. But I also didn’t write “as she was wearing” but only “as her”.
The problem is that as, like most English function words, serves more than one function: it is both a preposition, which requires the objective case, and a conjunction, which requires no case at all since it introduces a full sentence. (It can also function as an adverb, by the way.) Using as as a preposition, it is perfectly fine to say things like: “as big as me”, “as round as the moon”, “as important as him”. Using it as a conjunction, we can say, “as big as I am,” “as round as the moon is,” or “as important as he is.”
So, to begin with, we can say “Portia Carr was wearing the same dress as her (Maud)” or “Portia was wearing the same dress as she (Maud) was wearing.” Both are perfectly grammatical and normal. However, it is also true that repeated phrases are consistently omitted in spoken and written English. So “Portia was wearing the same dress as she (Maud) was wearing,” may be shortened to “Portia was wearing the same dress as she was” or just “as she.” Again, either is perfectly grammatical and normal.
The issue here is not which is right or wrong but which is preferable in any given context. In most US dialects, the preposition as offers the same comparative sense as the conjunctive as, so both as she and as her are correct and acceptable.
Not all dialects outside the US allow the comparative meaning of the preposition (it has two or three others, too). This means that as her would not be acceptable or correct in those dialects. As is so often the case, the preference here boils down to which dialect we prefer—or your own personal preference.