"We are not just dealing with a death. We are dealing with a terrorist attack. Even now its very surreal."
One reality check was seeing armed police in Auckland CBD on Friday, Gosse said.
"That doesn't happen in New Zealand."
But Gosse said Armstrong would be "over the moon" to see the public outpouring of love for her Muslim brothers and sisters.
Armstrong had always seen the good in everyone and the beauty in everything with a "childlike innocence", helping anyone who needed it.
"She befriended many travellers, immigrants and refugees opening her home, her heart and her kitchen," he said.
Armstrong loved sharing New Zealand with foreign arrivals, taking them to parts of the country they might never see otherwise and helping them to settle into their new home.
"She moved to Christchurch in recent years to be closer to her daughter and grandchildren - who at this time ask for space and to be left alone whilst they grieve."
Gosse and his brother have flown down to Christchurch to support their family.