The family of a mother who died suddenly weeks after giving birth due to an undiagnosed heart condition is urging mums to prioritise their health.

Sydney mother Cathy MacGuinness suffered a cardiac arrest at home on Easter Sunday and died in hospital almost three weeks after being placed in an induced coma.

Her sister-in-law Gillian Binchy-MacGuinness said the mum of three was suffering from dilated cardiomyopathy, which had nuanced symptoms including fatigue, shortness of breath and swelling in the legs.

She leaves behind her husband Sebastian Fletcher and their three daughters aged 7, 3 and five weeks old.

Ms Binchy-MacGuinness said many mothers could relate to never getting a full night’s sleep, often feeling exhausted and overlooking symptoms.

“What we really would love is for mothers in particular to make sure they put their own health first and go and get those checks.

“Cathy seemed to be the picture of health to all of us and for this to have happened, it is just such a tragedy.”

Ms Binchy-MacGuinness said there were no warning signs and the loss had forever changed the family.

“It’s been the hardest three weeks of our lives since we heard what happened on Easter morning, and it has been an absolute rollercoaster ever since,” she said.

“Seb has been pillar of strength for his daughters. He is supporting them and doing everything he can.”

Ms MacGuinness’ friend Joanna Allen set up a GoFundMe to support the family with their unexpected loss that has raised more than $155,000.

Ms Allen paid tribute to her friend, saying she was one of those rare people who always showed up with her full self and lit up any room.

“She turns up to climb whatever Mt Everest presents her with that day,” she said.

“She conquers it, then disappears in a poof of sparkle, off to find the next thing to say yes to. Leaving the rest of us thinking, ‘Wow … what a person’.

“She accomplishes everything she sets her mind to, looks incredible doing it and still makes everyone else feel a million bucks at the end.”

Ms Allen said Ms MacGuinness loved her family.

“Seb and her girls were her entire world, her greatest love, her proudest achievement, her reason for everything,” she said.

Ms Allen said like many young families, Ms MacGuinness and Mr Fletcher did not have life insurance because they had their whole lives ahead of them.

“So Seb is now facing the unimaginable – raising three daughters, one of them a newborn, while navigating grief and loss no person should ever have to face – all alone,” she said.

“We’re raising funds to help ease the immediate financial pressure on Seb. Every cent raised will go directly to Seb and the girls.”