Megan Robertson, of Burley, Leeds, had complained of crushing side-effects of anti-seizure tablets which came with the drugs - including dizziness, nausea and extreme tiredness, Wakefield Coroner's Court was told.
The teenager was found slumped in her bedroom on the day of her death after saying to her mother she was exhausted following a shopping trip.
The inquest heard how the schoolgirl suffered from frontal lobe epilepsy which invoked nocturnal epilepsy seizures, night-time fits.
Despite Megan suffering from seizures, pathological experts say they could not rule out an abnormal heart condition was the cause of the teenager's death.
Coroner Kevin McLoughlin read out evidence by specialist epilepsy nurse Janet Kellet to the court following the youngster's death on December 27, 2016.
He said Ms Kellet said Megan was only taking three out of seven doses of her carbamazepine medication in the weeks leading up to her death.
The nurse's evidence read: "Megan said she did not want to take her medication as prescribed because it made her tired.
"I discussed with her the risk of a higher frequency of night seizures and the risk of sudden death as a result."
Megan spent several hours on the day before her death in bed 'due to exhaustion' following a shopping trip with her mum Samantha Robertson.
She was found on the floor of her bedroom at her family home with her head resting on a chest of drawers by her sister Georgina at about 7.30pm.
Trainee nurse Georgina began CPR until paramedics arrived but Megan was pronounced dead upon arrival at Leeds General Infirmary at 8.20pm.
The inquest was told by Neurologist Dr Munni Ray that tiredness was a known side-effect of the drug.
She also said Megan's frontal epilepsy seizures were less frequent when she adhered to the correct dosage.
However, Megan's mum Samantha told the inquest: "She was not just tired - she couldn't walk down a corridor at school in a straight line.
"She couldn't go two or three nights without having a seizure.
"Megan was getting dizzy if she took the meds in the morning so she stopped taking them.
"If I could have made her take them I would have - but you cannot force a 15-year-old to take medication if they don't want to."
Addressing Dr Ray, Samantha told the court how her daughter had requested a different type of drug as she was still suffering seizures.
Dr Ray told the court how she had tried to arrange more tests to find out if Megan was suffering from a different type of epilepsy to help find a better drug.
However, Megan had refused any more consultations with Dr Ray and died some weeks later.
Pathologist Jens Sthalschmidt had told the corner how his postmortem revealed the teen suffered from an abnormal heart condition.
He told the court that the condition - myocarditis - had caused inflamation of Megan's heart which could lead to the heart stopping and sudden death.
The doctor confirmed that this could have killed Megan regardless of whether she had been suffering a seizure.
Coroner Mr McLoughlin concluded that Megan died of natural causes.
Speaking after the inquest, her mum Samantha Robertson, 47, said: "Megan liked make-up, music and going out with friends.
"She could be bolshie and an absolute madam - when things didn't go her way she would slam doors like all 15-year-olds.
"But she was a really funny kid with a great sense of humour.
"She was very popular and had hundreds of friends - many of them on Snapchat and other social media outlets.
"Megan was a gorgeous girl and is really missed - there was something about her you couldn't help liking even though you wanted to tear her to pieces at times.
"She was a big character and we never expected anything like this to happen.
"That night I just went into autopilot - it was just horrific."
Megan, leaves behind two sisters, Georgina, 25, and Francesca, 21, and two brothers, Keiran, 23, and William, 20.
Mum-of-five Samantha, who works as a head housekeeper at a dementia care unit, added: "Even a year on it's still exactly the same as it was the day it happened.
"Even now I will be getting ready to go out and just think 'I'll pop down and see if she wants to come - it's really hard.
"She had a really foul temper when things did not go her way and she got it in her head that the meds were making her poorly and wanted something else."
Megan's family is crowdfunding for Epilepsy Research UK and have raised more than £4,000 so far.
To donate, visit: justgiving.com/remember/410893/Megan-Robertson.