The couple, who had been married for 53 years, will have a joint funeral mass which will be watched remotely by their loved ones, before Arty is cremated and Isobel interred.
Describing her late parents as "great people who never had a bad word to say about anyone", Fiona said she and brothers Mark (43) and Chris (47) would attempt to make today's send-off as special as it can be, considering the highly unusual and distressing circumstances.
"My dad is being cremated, my mum buried," she told the Belfast Telegraph. "We can't be at the crematorium but luckily they're allowing us to be at the burial.
"The priest is going to say a Mass in the morning for them beforehand which we will be watching on Facebook at home before we head to the cemetery for 11am."
Fiona (40) spoke of her relief that her brother Chris, who lives in Kent, is in Northern Ireland for Saturday's funeral.
"We were worried he wouldn't be able to get a flight under the circumstances but he made it here," she said.
When Mr Vallely fell ill he was taken to the Royal Victoria Hospital, but when he tested positive for Covid-19 he was transferred to the Mater, now a specialist hospital for coronavirus.
He had been suffering from lung cancer.
His wife was taken to the Mater on Thursday, March 26 and died one week ago on Saturday.
Her husband died in the same room that she had, just hours later. She had suffered a stroke six months ago.
"I was very, very grateful (to the staff) that they let us do that under the circumstances, and we had to wear the protective gear and everything, because I know a lot of families haven't had that chance Fiona Vallely
Fiona told how she rushed to Belfast from her home in Tenerife six months ago when her mum had the stroke.
"We didn't think mum was going to pull through but amazingly she did," she said.
"She had a lot of health issues. She had two heart attacks, then she had a stroke, but amazingly she managed to pull through and was doing good considering.
"The last six months have been hell, even before this coronavirus.
"Dad became really ill and was diagnosed with terminal lung cancer, which was a real shock to us all. He's been in and out of hospital."
Ms Vallely said it brought great comfort to her that she had been able to say goodbye to both her parents in hospital.
"I was very, very grateful (to the staff) that they let us do that under the circumstances, and we had to wear the protective gear and everything, because I know a lot of families haven't had that chance," she said.
Fiona said losing both parents was a massive blow.
"We were just getting our heads round the fact that dad wasn't going to last much longer," she said.
"Up until a year ago he was always relatively healthy for his age, so we thought he would outlive us.
"My mum has been through so much and she always fought back amazingly but this she just couldn't fight.
"To lose both parents so close together in these circumstances is horrible. It hasn't fully sunk in and I don't think it will for a while."
We've made the best out of a very terrible situation. Once this madness is all finally over we will give them both the big send off that they deserve Fiona Vallely
Fiona, her brothers and "a few" family members will be at the funeral in person.
"A lot of our family are self-isolating and they're in the high risk category so they have to be very careful," she said.
"It's going to be hard and that's why we wanted to have a nice Mass that people can watch hopefully on Facebook.
"We've made the best out of a very terrible situation. Once this madness is all finally over we will give them both the big send off that they deserve."
Fiona described her mum, from west Belfast, and dad, an Ardoyne native, as "great people" who were "very different".
"Mum was a friendly, amazing woman," she said."She was very family orientated and very close to her two sisters.
"Dad was larger than life, a real character. Despite their age, they were both so young in their heads and hearts."
Fiona, who will be staying in the family home for now, soon hopes to return to her partner Ian (45) in Tenerife.
"He's been a great support," she said. "He loved my parents very much and they loved him.
"The reality of what has happened will hit us a bit more after the funeral but today is definitely going to be the hardest day ever."