The Belgian world number one, who captured the French Open last year against compatriot Kim Clijsters, has been sidelined with a virus but will open proceedings at Roland Garros against France's Sandrine Testud.
"I made the decision to play. We'll see how it goes," she said. "My goal is slightly different now. I've just decided to enjoy myself," she told a news conference on Sunday.
Henin-Hardenne said the break had been useful to find new energy and she felt in good shape as she aims to defend a grand slam crown for the first time.
"I feel all fuelled up now," said Henin-Hardenne, who has also won the the U.S. and Australian Opens since her victory in Paris a year ago. "I feel I was able to stand the workload it took to come back."
"During my illness, I felt like doing nothing. I did not miss tennis," she said, although she admitted coming back to Paris was "an extraordinary feeling".
"I'll feel very nervous before this match as I have had no matchplay for the last two months.
"Sandrine is a friend who has taken the time to have a baby girl and it's nice to see her back," she added of her 32-year-old
Henin-Hardenne singled out in-form Amelie Mauresmo as the tournament favourite after the Frenchwoman's recent victories in Berlin and Rome.
"She emerges as the favourite given her recent results but it remains a wide open draw," she said.
Mauresmo also starts her campaign on Monday on the Suzanne Lenglen court against Slovak Ludmila Cervanova.
In the men's draw, 1999 champion Andre Agassi meets French qualifier Jerome Haehnel just after the Henin-Hardenne opener while U.S. Open champion, and second seed here, Andy Roddick takes on veteran Todd Martin in the evening.
Third seed Argentine Guillermo Coria, the most successful claycourt specialist this season, also starts his campaign against Russian Nikolay Davydenko on Court 1.
Defending champion Juan Carlos Ferrero, still doubtful about his participation because of a rib injury, is scheduled to start on Tuesday against Germany's Tommy Haas.