Ah, the Helen Gordon on Deceased Online is the wrong one - she was buried on 10 February 1883 in a different section of Nellfield (there are 3), and was in Old Machar Poorhouse, as opposed to St Nicholas Poorhouse which is the one on Nelson Street, near Mounthooly where your Helen was. I think your Helen Gordon is in section 1, given the date of the burial of her child, as the other 2 parts of the cemetery weren't open then.
Given that there's no age or name recorded next to Helen's child, I'd imagine that it was possibly stillborn. Sometimes this is noted in the burial entry, but not always.
If you contact the Archives in Aberdeen (archives[AT]aberdeencity.gov.uk) they should be able to provide you with a map of section 1 of Nellfield, which shows where the lair is located.
As to the question of who she was married to - if she had been living apart from William for a long time, it could be that whoever registered her death didn't know his name, couldn't remember it, or simply got confused. Did her son James keep the last name Tawse throughout? Or did he change it to Christie, or Gordon?