Nicole Doherty said she feels "blessed" every single day that Evie is alive as she encouraged people to sign up to the organ donor register.
Evie Doherty spent so long in hospital waiting for a heart transplant that she could not remember what trees were when she was allowed to return home.
Her parents Nicole and Paul Doherty feared she would never come out of hospital.
Evie survived using a mechanical heart for more than seven months before receiving the transplant in early 2016 at the world renowned Great Ormond Street Hospital (GOSH).
The youngster suffered three strokes while using a Berlin Heart device while he was waiting for a new heart.
Now her mother has thanked the family of the organ donor, whose "selfless decision at a terrible time" means her four-year-old daughter can go to school like thousands of other children across the country.
She described her daughter as a "beautiful, smart, caring and cheeky little girl" and said it was "amazing" that her daughter's first day at school coincided with Organ Donation Week.
She told the Press Association: "I'm still in a bit of a dream about her starting school.
"When we were in hospital, we didn't even know if she was going to come out.
"All of these milestones that she is coming across and conquering, it's like a dream come true.
"We owe so much to the family of the donor - thank you will never be enough for the selfless incredible decision they made at their worst time.
"They have literally given Evie, and us, a life and you could never put into words how thankful you are for that.
"Every single day we feel blessed that they did that. Especially with her starting school.
"Evie is our only child and for your child to start school that had no health issues it is an emotional time but for somebody that you didn't know would even make school it feels like a miracle.
"I feel so incredibly blessed that she is able to do these normal things."
Mrs Doherty said she was "so so grateful" every single day Evie was alive, adding that the youngster was incredibly excited to start school.
"It will be really good for her to learn her ABCs and colours and numbers, obviously she was in hospital for nearly a year between the ages of two and three so academically she is behind her peers," Mrs Doherty added.
"When we came out of hospital she asked me what a tree was because she didn't know, she had been in hospital so long.
"There was pigeons in the park and she didn't know what they were.
"She knew stethoscope and echocardiogram but she didn't know what a tree was.
"She loves learning new things and taking them on board.
"She's really going to enjoy learning in general."
Mrs Doherty, 31, said she first noticed something was wrong in May 2015 when Evie's breathing became unusually fast. She called 111 for advice and they called an ambulance straight away.
Tests showed that Evie, who was two at the time, had a huge dilated heart and she was diagnosed with dilated cardiomyopathy, a condition where the left ventricle is enlarged and weakened.
The stay-at-home mother said: "It was an absolute shock that day.
"We were told that a third of children don't survive, a third need a heart transplant, and a third can be maintained on medication and sometimes the heart repairs itself.
"We just clung to the hope that Evie would be one of those who recover."
Initially, Evie was sent for care at the Evelina Children's Hospital in London where doctors tried to tackle her condition with medication.
She was then moved to GOSH where she was put on the Berlin Heart, which she used for seven months until she got her transplant.
Mrs Doherty added: "It was incredibly hard. Her life was hanging in the balance every single moment.
"I just cannot thank GOSH enough for their dedication for their fight for life for Evie.
"It was their fight for knowledge and Evie's fight for life that she got to a point where she could actually have the transplant."
While on the artificial heart, Evie suffered several strokes which left her without the use of the left side of her body.
After intensive physiotherapy Evie is now able to walk again with help but she has lost her left peripheral sight in both eyes and suffered damage to her kidney and spleen from the clotting.
Recalling the moment she was told a heart had become available, Mrs Doherty said: "You're full of conflicting emotions.
"One minute you're so high and ecstatic that this is happening.
"Then you think about the donor family and the selfless decision they are making at such a terrible time.
"You wonder how you can ever thank them enough.
"Someone has given her a life.
"There are no words that can express the gratitude you feel."
She said that she and her husband Paul, a 33-year-old printer, who come from near Colchester in Essex, were supporting the RBC Race for the Kids - a 5km course on Saturday October 7 in Hyde Park - to raise money for GOSH.
Mrs Doherty said she would also like to encourage people to sign up to the organ donor register.
She said she also supported "opt out" organ donor systems.
:: To find out more about the GOSH fundraising event visit www.raceforthekids.co.uk