I have found the following in our National archives. These are all estate files. Going on your information I think that possibly the first two do not relate to your Mary Ann, as the second one says 'born in London, however the third one spells her surname as Stuart! If you wish to order a file I suggest you do it through eggsa.org. Hope this helps and does not add confusion!
DEPOT NAB SOURCE MSCE TYPE LEER VOLUME_NO 0 SYSTEM 01
REFERENCE 17756/1932 PART 1
DESCRIPTION MCEWEN, JAMES GARDINER. (S/S MARY ANN, BORN STEWART).
STARTING 1932 ENDING 1932
DEPOT NAB SOURCE MSCE TYPE LEER SYSTEM 01
REFERENCE 740/1960 PART 1
DESCRIPTION MCEWEN, MARY ANN. BORN STEWART. BORN IN LONDON, ENGLAND. PRSP
MCEWEN, JAMES GARDINER. NO TRACE. DECEASED ESTATE.
STARTING 19600000 ENDING 19600000
DEPOT TAB SOURCE MHG TYPE LEER VOLUME_NO 0 SYSTEM 01
REFERENCE 3125/43 PART 1 DESCRIPTION GARDINER, MARY. BORN STUART.
STARTING 19430000 ENDING 19430000
REMARKS PREDECEASED SPOUSE JAMES GARDINER