Question: Q: Martha Williams, 26, travelled to the UK to donate stem cells to 24-year-old May Brown.
The Home Office reversed a decision not to issue Ms Williams a visa after more than 60,000 signed an online petition.
The transplant was deemed a success in March. But the African Caribbean Leukaemia Trust (ACLT) said Mrs Brown died on Friday following a relapse.
It added she passed away "surrounded by her loved ones".
The operation was postponed from December to January after Mrs Brown, from Weymouth, became unwell with a virus and required further chemotherapy, ACLT said.
However, ACLT co-founder Beverley De-Gale said Mrs Brown relapsed in April.
"The leukaemia came back and it came back very aggressively.
"The doctors tried again to get May back into remission but sadly the leukaemia was too strong."
She added she felt the delay in Ms Williams getting a visa may have contributed to Mrs Brown's death.
"You never know with any cancer what way it's going to go but any delay is never going to help the situation.
"I sadly have to say that could be a possibility but I am not a medical expert."
King's College Hospital in London, where Mrs Brown received her treatment, refused to comment on the matter.
However, a spokeswoman said staff were "saddened" by her death, adding: "Our thoughts are with her family and friends at this difficult time."
Mrs Brown was diagnosed with leukaemia in July 2015.
She had been told her only chance of survival was an urgent stem-cell transplant. Her sister Martha was a "10 out of 10" tissue match.
ACLT said Ms Williams was initially refused a UK visa because her teacher's salary of Â£222 per month was too low.
Mrs Brown is survived by her husband Mike and two-year-old daughter Selina-May.
Paying tribute to his wife, Mr Brown said: "May will forever be remembered in our hearts.
"She was a strong, beautiful, supportive, wonderful wife and mother. Selina and I will truly miss her."
In a statement, the Home Office said Ms Williams' visa was issued on compassionate grounds on 21 October.
A spokesman said the visa was initially refused on 5 October because she did not meet the requirements of the immigration rules.

A: A woman with leukaemia at the centre of a campaign to allow her donor Nigerian sister to come to the UK has died.


Q: The 27-year-old, who counts Fortuna Sittard and Rapid Bucharest among his former clubs, joins the Championship club on a one-year deal.
"I am here to score the goals that will help this club win the title. I look forward to showing the fans what I can do," Nkoyi told the club website.
The striker is boss Ray McKinnon's fifth signing of the summer so far.
James Keatings, Billy King, Thomas Scobbie and Paul McMullan have already signed on at Tannadice and McKinnon believes Nkoyi, who last played for MVV Maastricht, will have a major impact.
"Patrick is a big, strong, athletic goalscorer," the manager said. "He has good pace and can score with both feet. He will add to our attacking threat and offers a different impact to the attackers already here.
"I am delighted with this signing, and I believe he will become a big favourite with the United fans."

A: Dundee United have signed Congolese-Dutch striker Patrick Nkoyi subject to international clearance.


Q: The England opener produced a gritty performance, bringing up his 50 off 154 balls, finishing unbeaten on 77.
A brilliant 97 off 92 balls from Alex Davies saw the visitors reach 314-5 at the close, giving them a lead of 239.
Earlier, Liam Dawson made 75 but the hosts were bowled out for 224, a lead of 75, as Kyle Jarvis took six wickets.
Hampshire had resumed on 147-5 and England all-rounder Dawson went on to score his second Championship fifty this season before being bowled by Matt Parkinson.
Jarvis then trapped Ian Holland lbw, had Gareth Berg caught at third slip before Kyle Abbott and Mason Crane edged behind, giving the Zimbabwean impressive figures of 6-61.
After making just six runs in the first innings, 20-year-old Hameed - who won three England Test caps over the winter - struggled for fluency at the start of his innings but then built in confidence.
In stark contrast Davies attacked from his first ball, smashing 16 fours and a six before he fell three runs short of his century as he was caught at slip off Dawson.
Hameed, with the England selectors watching ahead of the three-Test West Indies series, dug in and hit 10 fours and faced 219 deliveries in total to put the visitors in a commanding position.

A:
Answer: Haseeb Hameed scored his first half-century in the Championship this season to help Lancashire take control against Hampshire on day two at the Ageas Bowl.