Suzanne Green and Tracey Warnast have been friends since their daughters were at primary school together in Medway.
Now Tracey has given Suzanne one of the biggest gifts a human being can give to another - the chance to live.
Suzanne had been undergoing kidney dialysis for four years and her health had been deteriorating.
Each session took such a toll that her elder daughter, Savanna, 16, had taken on caring for her younger sister Kizzia, 11, to help her mum.
She had been told her only option was to have a kidney transplant.
But her donor came from somewhere she had not expected: Tracey, mum of Becky, one of Savanna’s best friends from St Thomas More Primary School, Walderslade.
Suzanne said: "One night, I went to pick up Savanna and she just asked me about it. I told her to contact Canterbury hospital, but I didn’t think any more of it.
"Then months later, I went to pick up Savanna and she said she’d passed the test. I said ‘What test is that?’, and she said: ‘Hasn’t anyone told you? I’m your donor!’.
"I just burst into tears."
The pair had to prove that she was giving the kidney without being paid and the head teacher at St Thomas More helped by vouching for them.
The transplant took place at Guy’s Hospital in London and Suzanne,of Barming, near Maidstone, was discharged a week later.
She said: "She [Tracey] is a diamond. I’ll never, ever be able to repay her for it. We have become very, very close.
"There aren’t words to say how I feel about her, but she’s one in a million."
She said: "It will make such a big difference to all of us. I’m looking forward to taking the girls swimming and to theme parks, as I couldn’t do things like that before.
"I’m going to be able to help my parents more, and it will be a huge change to Savanna, who used to stay home to help me, but she’ll be able to go out more and have fun.
"It has changed our lives."
Another way it has changed Mrs Green’s life is that she is much lighter now having had to lose 10 stone before she was allowed to have the transplant.
The single mum started dieting in 2010 when doctors said it was necessary in order to have the op.
It took her 14 months to shed the extra weight. She said: "I did have a lot of help from a dietician. It was very hard though.
"But once I started to lose some of the weight, I felt better, and I was much happier, so it became easier.
"I am much more mobile too now."