But she warned the master is up against the apprentice - with GB team-mate Katarina Johnson-Thompson also a possible winner.
And they face chief competition from Canada's world number one Brianne Theisen-Eaton. For UK timings f the event, starting today - Friday, August 12 - see below.
Double Olympic gold legend Kelly, aged 46 - an 800 metres and 1500 metres winner - believes wins by Jess, 10,000 meters champ Mo Farah and long jumper Greg Rutherford will see a repeat of 'Super Saturday'.
She said: "We have some of the best athletes in the world ever in Great Britain and the heptathlon is going to be a great competition with Jess up against Katarina, who is unknown to many people but in the world of athletics, she's there or thereabouts.
"Katarina messed up in the World Championships last year, so I think she's one that is going to be at her best.
"But who will win? My assumption is Jess, if everything goes well. But there are seven events and anything can happen. Jess is a stalwart, she's got the experience to pull it off again.
"We've seen already at the Games that some of the established athletes are not pulling it off, coming fourth and fifth, while the new ones, the underdogs are pulling through. So who knows?
"We've also got Greg Rutherford in the long jump - Olympic champion 2012 and he seems to be in the form of his life. He believes he can win it again, I think he's got it, he can do it
"And of course Mo Farah. If he pulls off the double double, that would be extraordinary and he would have more medals on the track than other British athlete.
"You just never know.You always want to put your money where your mouth is and say they are definitely going to win. You would not write off those three in particular.
Kelly aded: "Sheffield is very special to me. I used the EIS - a really great structure for athlete that need that support system. I've also run education programmes from the EIS and Sheffield was my last race ever when I retired. I was dropped in by helicopter. I'll remember it always."
Ennis-Hill herself admits it would be "incredible" to be part of a repeat of 'Super Saturday' at the Rio Olympics.
The 30-year-old will begin the defence of her heptathlon crown at the Olympic Stadium today - Friday, Augut12 Friday, with the culmination of the seven-event competition coming the following day, when Mo Farah and Greg Rutherford will also go for gold in the 10,000 metres and long jump respectively.
Four years ago in London the trio gave British athletics its finest hour, all three celebrating victory on home soil, to the delight of a frenzied crowd, within the space of a barely-believable 45 minutes.
The timetable this time means the medals cannot be won in quite such a short space of time, but there remains a strong chance of another momentous day.
"It is really exciting. I am happy the timetable has fallen like that," said Ennis-Hill.
"It's a really nice moment to be in the stadium again, knowing what we all achieved four years ago.
"It would be incredible to achieve it again, but I'm not sure if that's possible or not.
"I'm not going to be too greedy and imagine it will happen again, but it was really special to be part of that."
Of the trio Ennis-Hill has certainly experienced the toughest route to Rio, looking to retain her crown just two years after the birth of her son Reggie.
Should she be successful, she would become only the third athlete - after Australian sprint hurdler Shirley Strickland in 1956 and Cameroon triple-jumper Francoise Mbango Etone in 2008 - to win Olympic gold, have a baby and then return to successfully defend their crown.
Ennis-Hill flew in to Rio on Saturday after opting to miss the Team GB training camp in Belo Horizonte.
Instead she geared up for the Games in Europe - she declined to say where, only that it was "nothing glamorous or exciting" - in order to minimise the amount of time she would have to spend away from Reggie.
She had to overcome an Achilles injury earlier in the year, but is now feeling "fit and healthy" and is inspired by the chance to create memories in Rio that Reggie can treasure.
"It was so nice having him there (at her training camp), coming down to the track and doing his little bit of hurdling alongside me," she said.
"Every time I ran, he was going, 'Mummy, go, go, go'.
"He's aware of everything now, he knows what mummy does, he tries to copy what I do.
"He will have all those memories, DVDs, pictures, to look back on.
"I would love my performances to be great out in Rio, to show what him what his mum achieved just two years after he was born."
Ennis-Hill is also looking to become the first British woman to retain an Olympic title in athletics.
"I see it as a massive challenge for me," she said.
"Last year (when she won the world title in Beijing in her first major competition since giving birth) was a massive challenge and I feel like the odds are a little bit against me because it's a huge thing to achieve.
"But it's a really amazing position to be in.
"I relish this opportunity to go out there and see if I can do something really amazing at this stage in my career."
Her chief competition in Rio will come from Canada's world number one Brianne Theisen-Eaton and team-mate Katarina Johnson-Thompson, who looks to be over the long jump troubles which threatened to ruin her chances.
"Mentally, I've got to be 100 per cent focused," said Ennis-Hill, who fired out a warning of her own by running her second fastest time ever in the 100 metres hurdles - 12.76 seconds - last month.
"Physically, I'm going to have to be at the best I've been for the past few years.
"I've just got to hold everything together and know that I've done this before and that I can do it again."
Heptathlon schedule Day 1: Friday 12 August (all UK times)
100m hurdles: 1.35pm, live on BBC2
High jump: 2.50pm, live on BBC1
Shot put: 00.35am, live on BBC1
200m: 02.05am, live on BBC1
Heptathlon schedule Day 2: Saturday 13 August
Long jump: 3.45pm, live on BBC1
Javelin throw: midnight, live on BBC1
800m: 02.50am, (Sunday) live on BBC1