Thanks Leandra
Back then the chances of someone from the Glens meeting someone from Lisburn while in Ireland would have been relatively small - it's a hour by motorway and main road even today. That said, on a steamer or in a new country their accents would soon have placed them in a smaller and more recognisable group. Not an uncommon state of affairs I guess.
I still reckon that it's the wrong Nellie/Ellen/Helen as according to the grave photograph she was born in 1885, not 1890. I don't think anyone would get it that wrong, especially on a grave. That coupled with the full name in the marriage entry make it very unlikely.
Maybe in years to come some link between the Newells in Canterbury and the Nellie I seek will emerge. Thanks though Leandra for the details as if further information emerges I'll at least know to be wary of POB 'Ireland' entries.
All the best
Christopher