I don't know, it is an interesting thing she has been absent from the games, maybe it is to give Link this kind of 'special' status, then again, he has had a sister which kind of take away the only kid and therefore special, hahahah.
I dunno, it would be odd, just like having the sister was odd when first announced but it could be pulled up nicely. After all if Link could leave grandma, he can leave mum too if required to full fill his destiny. Maybe it will make it awkward if link decides not to return in the end when it is her mother the one waiting instead.