Her sister Lisa, 24, of Whitehaven, has set up an online crowdfunder to raise the money to give her a dream wedding and then use the excess money to later take the pressure off the grieving family and pay for her funeral.
She said: "The diagnosis was a real shock and Susan is petrified; she's scared of going to sleep and not waking up.
"The chemo can't cure her cancer but it can prolong her life and keep her out of pain."
Susan and Jay, 38, have been together for many years and the thought of being able to fulfil their wedding dream has provided a ray of light during these tough days.
"They're definitely a loving couple," Lisa continued, "and Jay has really stepped up and is doing an amazing job at looking after the children while Susan is in hospital.
"I can't believe how generous people have been.
"My experience of life and people hasn't been great, but for everyone to show us all this love has really changed my view of the world.
"It has definitely picked Susan up too; it's something to look forward to. Someone has offered to go to hospital and show her some wedding dresses, which is beautiful."
The appeal has already raised £5,300 in less than a week.
Ms Rumney's diagnosis comes towards the end of an already tough year, after her mother died suddenly in January.
Lisa said: "I barely leave the house due to my anxiety and mental health, but this is about Susan and what we've got to do for however long she's got - we know the cancer will beat her."
Her sister started having a pain in her leg at about the time her mother died.
She sought medical advice and doctors initially put it down to a blood clot, before later changing their diagnosis to sepsis.
But two weeks ago she found out the real cause of her pain - and with it the devastating diagnosis.
Lisa said: "The older children know that she has cancer, but the younger two don't really understand.
"They just know she's poorly and goes in and out of hospital. It's heartbreaking."
