She was joined by her intended climbing partner, Alan Hinkes, when they left Britain on 11 June, reaching Base Camp two weeks later after a 10- day trek from the nearest settlement.
The remoteness of the Himalayan peak, in comparison with Everest which is only a two-day walk from the closest village, merely adds another layer of difficulty to what climbers regard as the toughest ascent.
A note from Ms Hargreaves, which has just reached her family by fax from Scott Fischer, an American in the party who returned earlier, gave a picture of her progress until a week before Sunday's scaling of the peak.
She and Mr Hinkes reached Base Camp on 25 June and left for Camp Two, but Ms Hargreaves decided to join up with an American climber, and he teamed up with someone else.
For the next weeks she climbed higher and then moved back down again in order to test her equipment and to acclimatise herself to the altitude.
"That is quite normal in climbing," said Cally Flemming, marketing manager at Nevis Range Ski Centre in Scotland, where Ms Hargreaves was based. "There had been concern that she had lost some of her fitness in the two weeks she was home."
But by 18 July - having left the American at Camp Two - Ms Hargreaves, climbing alone and without oxygen, had reached nearly 8,000m, 600m below the summit, when she was forced back by the weather.
Mr Hinkes, who by then had teamed up with two Dutch and two Pakistani climbers, reached the summit. Yesterday, he said he last saw Alison Hargreaves on 23 July when she had been forced to return to Base Camp because of worsening weather - just before he left for Britain.
Fierce and unpredictable storms pinned her and the others in Base Camp for five days. But by 31 July the conditions had improved and, according to the fax, she "started clearing her ropes and breaking a trail" to 6,000m, where she rested at Camp Two the following day.
Two metres of fresh snow had fallen on Camp Three, burying the tents and equipment, by the time she arrived there at 7,200m on 3 August. Yet, after digging out the camp, she was once again forced to descend by the deteriorating weather.
In the note that she wrote on 6 August, she explained that she was feeling fit and had rested for a couple of days, but was becoming increasingly frustrated by the treacherous weather.
"She wrote that she was going to go for it if the weather improved," said Ms Flemming. "She regarded that as her last chance on this trip." It seems that during the week the climbers managed to move higher and by last Sunday morning they left one of the higher camps for the summit.
Reports suggest radio messages intercepted at 6pm by other climbers say Ms Hargreaves, an American, Bob Slater, thought to be her climbing companion, and Bruce Grant, a New Zealander, had reached the summit and were descending.
What happened next could take days to unravel.Reuse content