Gracie Mackay lost her fight for life on Monday in the Royal Hospital for Sick Children in Glasgow, where she was flown after being found unconscious, face-down in the waters of Loch Gairloch, Wester Ross, on Sunday.
Ewen Beaton, 32, of Beauly, Inverness-shire, is feared drowned after his sons Jamie, two, and five-year-old brother, also Ewen, died in hospital following the tragedy during a day out for the two families in a narrow Canadian-style canoe.
Gracie's relatives said in a statement: "Grace was a funny, caring, thoughtful daughter and granddaughter, full of life who loved animals and being outdoors.
"She adored her family and was our beautiful angel. We are devastated by the loss of our best friend."
The search for Mr Beaton was called off again last night, but Northern Constabulary said it would start again this morning and continue "for the foresee-able future."
Gracie's sister Callie, eight, who swam more than 550 yards ashore with her father Garry Mackay, 36, to raise the alarm, was only told yesterday at a family gathering that Gracie had died.
Her grandfather John Mackay, of Inverness, added: "When we were in the hospital we thought there was a little bit of hope that Gracie could pull through, but it never happened."
He said his son Garry is "in a hell of a state, the whole family is".
He talked of the close friendship Garry had with Mr Beaton.
Mr Mackay said: "They had been fishing literally thousands of times together.
"They had been hill climbing all over the Highlands together. They both doted on the children and they took the kids on outings like this on a regular basis.
"They had been on boats many, many times together and I believe they had been out on the canoe many times together. They had been on a day-trip together, but we don't know if they had had the kids out on the sea before."
Tracy Sinclair, Gracie's headteacher at Tarradale Primary School in Muir of Ord, also paid tribute to Gracie, who had just entered her second year. Callie is in primary five.
Ms Sinclair wrote to parents, urging them to support the family: "It is with great sadness that I write to inform you of the death of a P2 pupil from our school. Gracie Mackay was a happy, thoughtful little girl who was popular and well liked by everybody. This has come as a shock to the whole school community and we are all deeply saddened."
Gracie, Callie and their father had been with the Beaton family in the canoe, just off the Big Sands beach near a caravan site, when it capsized on Sunday afternoon.
Weather conditions were described as perfect, but senior members of the coastguard have questioned the stability of the craft with six people on board.
Canoe experts have also highlighted the absence of a second canoe, which could have been used as back-up in the event of an accident.
The two young Beaton boys were airlifted to Raigmore Hospital in Inverness, where they later died.
The villages of Beauly and Muir of Ord are just three miles part, on either side of the Inverness-shire/Ross-shire boundary.
Local councillors talked about the effect of the tragedy on the small communities.
Graham Mackenzie, the former headteacher of Dingwall Academy who is now an SNP councillor for the area, said the impact was profound, but local people would rally round and support the families.