Ms Bateman, who works as a dental hygienist at Dental Solutions Tauranga, blurted out the offer while Ms Egglestone was serving her breakfast at Cafe 359.
"I had no intention of doing so, until the words came out of my mouth. But once they did, it felt entirely right.
"All I want is for Frankie to be well again. To me it's a no-brainer. I have a spare kidney, and apparently it's quite healthy. Frankie's my friend, and I love her, and I don't want her to die. I want her to be around for as long as humanly possible."
Ms Egglestone said she was stunned at the spur-of-moment offer.
"My jaw just dropped. I couldn't believe it.
"Lianne was one of my regular customers and I used to always make her a mocha, a damn good cup of coffee if I say so myself. She was effectively a person off the street until she became one of my regulars and we became close friends."
Initially Ms Bateman was not a match.
But after Ms Egglestone got gravely sick again last November, she said her mother flew from America to be at her hospital bedside, and pleaded with doctors to do something.
Her "amazing specialist" Doctor Pandi went back through the tests and found Ms Bateman had narrowly missed out on being a match.
The specialist retested the women in March and because the antibodies in Ms Egglestone's blood had dropped sufficiently, Ms Bateman was now a perfect match.
Ms Egglestone said when she and Ms Bateman got the news last Thursday that their operations would go ahead at Auckland Hospital on October 5 she was "elated and excited".
"Doctors told me that if did not get a kidney soon, I was not expected to live beyond the next two years."
It had been a "very tough" five year journey to get to this point, Ms Egglestone said.
She has been admitted to hospital twice for life-saving surgeries since November.
"During my last hospital stay I was in such excruciating pain, I pleaded with my dad to let me die," she said.
Ms Bateman said she had not discussed her plans with her family or friends at the Salvation Army church beforehand, but most people were incredibly supportive of her decision.
"Especially my two daughters and my dad who is now seriously considering becoming a live donor himself."
"It's entirely doable. You don't have to be a family member, or the same blood group, even complete strangers can donate organs.
"I've got the easy part as 70 per cent of my operation will be done by laparoscopy [keyhole surgery] and after a period of post-operative recovery I should be back home again within 10 days."
Both women said they were keen to share their story to encourage more people to become live organ donors, as one donor's organs could save "5, 6, or even 7 lives".
Now calling themselves "kidney sisters", the pair planned to get matching tattoos to mark the life-changing moment.
"I'm so grateful," Ms Egglestone said.
"All I want to be a normal healthy mother for my seven-year-old daughter Lexi and be there to see her grow up and have children of her own. I want to be a grandmother, and maybe a great-grandmother, and do all the normal things other people can do.
"It's a remarkable gift. It's pretty amazing as Lianne's kidney is literally going to save my life," she said.
Kidney donations
At least 2370 Kiwis rely on life-saving dialysis
Average life expectancy of patients was 3-5 years.
People waiting for a kidney from a deceased donor
could wait up to seven years or even more.
In 2014 there were only six kidney transplants
performed on Bay people - only 3 from live donors
In the past decade there were 389 deceased organ donors in NZ
Sources: Organ Donation NZ, Live Kidney Donation Aotearoa
Kidney Society New Zealand
