Susan McLay (24), since late last year has been working with the Hope for Homes Mission at an orphanage for children with special needs in the San Antonio Aguas Calientes area, less than 20km from the volcano.
The area was one of those most affected by a volcanic eruption on Sunday. That blast has been followed by smaller eruptions.
Ms McLay said she had stayed at the orphanage and part of her job was making sure the children were "OK and still able to breathe" with the ash in the air.
"The main priority has been to find survivors and rescue as many people as possible. Everyone just gets on and helps each other here. It is amazing to watch," she said via email yesterday morning.
"My plan currently is to help at the orphanage and [help] anyone that needs aid that comes to our town."
The death toll has risen to about 100. Hundreds are still unaccounted for.
In the days leading up to the eruption, Ms McLay said she noticed the volcano was "a little more active than usual", glowing orange and red in the night sky.
Initially, when she watched the eruption on Sunday with a co-worker, she was impressed rather than afraid.
"Massive billows of smoke were constantly being puffed into the air and taken for miles and miles over the mountains and into the surrounding areas," she said.
The next day was "probably the hardest day I have ever woken up to", she said.
"In our town we still had running water, and complaining about all the ash everywhere was easy for a split second until I remembered that there were villages, whole communities sitting under mud right now."
Ms McLay said the situation was made worse by heavy rain on Tuesday creating landslips and flooding and causing other towns to be blocked off and evacuated.
