The British multi-eventer has shown real resilience to come back from a foot injury which ended her hopes of reaching the 2008 Beijing Olympics and has since become a driving force in the heptathlon.
After the disappointment of losing her world title in Daegu, South Korea, the 25-year-old took some time off to recuperate and is now back in full-time winter training as she embarks on her quest to become Olympic champion.
"Nothing is guaranteed," Ennis's coach Toni Minichiello told BBC Sport.
"Heptathlon is a tricky sport. It's never a full-blown formality that Jessica's going to be picked [for the GB 2012 squad], she still has to go out and put in a performance good enough to qualify."
Ennis will compete at numerous indoor events in early 2012 as preparation for the London Games, including the UK Indoor Trials & Championships in Sheffield and the Birmingham Grand Prix, both in February.
The Sheffield athlete then plans to head to Turkey to retain her world indoor pentathlon title in March. Her only outdoor heptathlon before next summer will be at a meet in Gotzis, Austria, which she won last year.
Ennis began her winter schedule at the start of October. She trains six to seven hours-a-day, five days-a-week, in addition to a three-hour session once a week.
"It's pretty full-on and non-stop," says Minichiello, who has coached Ennis since she was 11 years old. "There's not much recovery between sessions."
Running, weights and circuits are the order of the day. This high-intensity schedule is expected to build Ennis's base fitness before her competitive season starts.
Ennis explained: "The disappointment in Daegu definitely motivates me, the real need to get that gold medal back. I'm trying to get into the best possible shape for next year."
While Ennis was almost seven metres off her best distance at the Worlds, it is not as bad as it may seem. She threw 45m in the warm-up minutes before the competition started but was let down by a number of "external factors", according to Minichiello.
Much focus was devoted to Ennis's Worlds performance in the javelin, but it should not be forgotten she also equalled her personal best in the long jump and set new records in the shot put and 800m.
Moreover, her points total of 6,751 was 20 better than that of her 2009 victory and her third best score ever.
"It's not really about improving in the javelin, I know where it needs to be - it's been there for the past couple of years," Ennis said.
Russian Tatyana Chernova, who took Ennis's world crown by 129 points, won an Olympic bronze last time around and will be a main threat to Ennis at her debut Olympics.
Reigning Olympic champion Nataliya Dobrynska could also mount an outside challenge but Ennis has beaten the Ukrainian multiple times in recent years.
The Briton could face a challenge much closer to home in Kelly Sotherton, who has decided to return to the heptathlon for London 2012, but the 35-year-old has not competed in the event since 2008.
"All the other heptathletes around the world are training really hard so I want to be training just as hard. It's always good to have rivals." Ennis concluded.