Ms Davies added: "I didn't think we'd win but, when you feel everything is shining down on you, you just go for it."
Her daughter bought the tickets from the Overmonow Garage in Monmouth, Wales, and was stunned when she checked the numbers in the early hours of Sunday morning.
Ms Davies, an admin assistant, and Mr Reynolds, a company regional director, were in the US to see his daughter graduate and for Ms Davies' operation.
She was diagnosed with a tumour on her parathyroid gland earlier in the year - and had arranged keyhole surgery at a world-leading treatment centre in Florida.
Sonia said: 'What a rollercoaster of a week we've had. I had my operation on Wednesday and until then we didn't know how serious it was.
"They told me that if it hadn't been removed it would have been fatal - and at the very least I would have lost my voice within a year.
'They managed to give me the all clear straight after the operation, so as you can imagine we were on cloud nine.
"Excited we were about to return home to celebrate our brilliant news, Keith was scanning his emails and read about the EuroMillions rollover."
She added: "He was convinced that we were the luckiest people on the planet and definitely on a winning streak after the success of my op.
"So we called up my daughter Courtney to ask her to go and buy us a ticket.
"She was travelling and wasn't able to change her plans so we called Stephanie instead as something told us we needed to get a ticket - and the rest is history."
Ms Davies was previously widowed aged just 47 when husband Malcolm died of leukaemia more than five years ago.
A neighbour at their home near Monmouth said this afternoon: "Sonia has been through so much and she is finally due some happiness.
"Finding the tumour must have been very frightening for her, especially after going through what she did with Malcolm.
"She kept news of her health very secret because we didn't know anything.
"But I'm glad she's got the all clear and to get win the lottery as well must be the icing on the cake."
Describing her dash to get the tickets, daughter Stephanie said: "My car was blocked in the drive by my boyfriend Steve's, so to save time I made him drive me to buy a ticket instead of moving mine."
She and Mr Powell did not check the tickets until the early hours of Sunday morning, after spending the evening with friends.
Mr Powell said: "We were laughing and joking about the lottery.
"Steph remembered she had bought a ticket. She said 'if I shout down it means we've won the lottery and if not, I've gone to bed'. She came down crying."
Miss Davies had checked the numbers on her iPad and realised they had all of them - with one UK ticket holder scooping the £61m prize.
She said: "As soon as I saw that ticket I had my hands over my eyes, I was shaking, I was crying.
'I said to Steve "for once in my life I am not even joking". We checked the ticket about ten times over.'
She then phoned her mother, who was waiting to board her delayed flight home.
Mother Sonia said: 'All I could hear was Steph sobbing down the phone and the odd muffled word. I thought she'd told me she'd lost her dog. Then I heard Steve shouting "we've won £61 million".
'We put them on speaker phone so Keith and I could both listen, but realised everyone in the airport could hear so we huddled round a bin while we checked the numbers and realised we really had won.
'I can remember saying "if we don't make it home just make sure you spend it all". It was the longest flight of our life.'
Stephanie then phoned up her sister Courtney, the fifth member of their syndicate, to break the news at 1.45am.
Describing their conversation, Courtney, who is studying psychology at the University of Southampton, said: 'We kept repeating "oh my God" to each other, over and over.
'In the end we had to say bye and hang up as we were so in shock we weren't actually talking to each other.'
The family - who hail from Monmouthshire in south east Wales - said they were still considering what to do with their £12,220,488 shares of the £61,102,442 jackpot.
Stephanie and her partner bought their first home together at Christmas so they plan to finish decorating the bathroom and may take a trip to the Caribbean.
Courtney wants to complete her degree before deciding what to do next but said she is planning on buying an electric toothbrush and a new car to replace her VW Fox, which has wind-up windows and no air con.
Her boyfriend Kieran, a student at Reading University, is hoping she will get the leak in his car fixed.
Ms Davies and Mr Reynolds will share their win with family and friends - though she would like a new oak-framed carport for their home.
