The 44-year-old mother of two died on June 3 after the car she was driving plunged into the River Lee at Kennedy Quay in Cork.
Her two sons aged 10 and 12, were passengers in the car, but managed to escape the vehicle as it sunk.
Gillian's body was later recovered from the vehicle once it was removed from the water.
At her funeral mass in Milltown, Co Cork on Tuesday, her grieving brother Jason read a heartbreaking tribute to the popular teacher on behalf of her husband John.
“There isn't enough time, and there aren't enough words to do justice to the lifetime of joy and happiness that you brought to the people around you and especially to me and to our two beautiful children,” his tribute began.
“You did me the greatest honour by agreeing to marry me, and our wedding in 2009 was the happiest day in our lives at least until [our sons] arrived in 2010 and 2012.”
“As with everything else you took to motherhood like a duck to water.”
“There has never been two children who have been as cherished and loved by their mum as our two handsome boys,” the eulogy continued.
“You've raised two fine brave young boys and the values you instilled in them will make it a very easy job for me to finish your life's work and raise them to be young men any mum would be proud of.”
John’s fond memories of more than 20 years with Gillian included many trips around the world to Asia, America and beyond.
“You loved to travel so much and we made so many wonderful memories journeying around the world.”
Detailing their trips around the globe, John said that his wife's “gentle and kind way transcended nationalities and language barriers” as she made friends wherever she went and brought out the best of people.
“I often stood back to watch you interact with people and shook my head in wonder at your ability to make a connection with a stranger within moments of meeting them, and put them instantly at ease in your company,” he shared.
Gillian’s brother said that the outpouring of love for her over the last few days since her untimely death have shown that she touched everybody who loved her.
“Gillian you had a heart of gold who lived your life for your sons always worrying and caring about them,” he said.
“Your gentle nature lives on through them and will forever more.”
“We will try and find comfort knowing your precious aunty Anna who only passed away recently is waiting for you with open arms.”
“To Gillian’s sons,” he continued.
“You are the most kind, caring and wonderful boys but now you are also the bravest boys we know.”
“Your kind caring nature is a testament to the way Gillian and John have raised you.”
“We all love you to pieces and we will always be there for you and your dad.”
He finished up the eulogy saying: “Goodbye for now to our sweet caring loving and beautiful Gillian.”
During the mass, symbols of Gillian’s life were placed on the altar.
A picture of her two sons, a travel book and children’s art work were all presented as symbols of her love for her children, travel and her students.
Other items symbolised her “loyal and true” friendship, her love of socialising and her love of the arts and literature.
She is survived by her husband John, her two sons, her parents, sister Caroline, brothers Jason and John, parents-in-law Martin and Eileen, brothers-in-law, sisters-in-law, uncles, aunt, nephews, nieces, neighbours, relatives and her many friends.