Good one, polarbear, I had not looked closely at the age rage of Elizabeth to Alveretta, just to Mary anne... I had checked the 1881 & it only gave me an Alveretta Brown in Ontario 1881...
(Whose eldest sister was born in Nova Scotia so something to look into, carricknew, if this bunch is yours...) or are you saying she was now a Martin? That would indeed make sense then that she might also be an offspring...
adding: I'll post the 1881 where she is now surname Martin
http://data2.collectionscanada.gc.ca/e/e325/e008116937.jpgSo the mother may have been married to a Sullivan, ( Mary Anne was down as Scottish ancestry 1871) then a Brown, the children taking on the surname. I'll look around for the marriage for Alveretta, silly me I was looking under Brown...