I've just had a look at the full page, and the ones immediately before and after. If anyone else wants to, it's at RG12/4591 fo116 p3 (Wales) - image quality varies from site to site, and the one at The Genealogist is very good.
I asked earlier about 'g' and 'y': every 'g' that I saw had a totally closed upper part, unlike the one here.
Uppercase 'A' - admittedly the majority are written like a large lowercase one, but the page before has a similar 'A' in Annie. Having said that, the entry we're looking at has a different inconsistency - the 'M' in Mother is different from the others.
Anyway, having seen the clearer entry I have no doubt at all that it's Mary A. It's also more evident there that the enumerator has a habit of putting a full stop or comma after names and initials, and on a blurry copy that can lead to confusion.
Mary's age is also a lot clearer - 34.