This is all true.
Funny though: I was indirectly watching a Tennis Channel special on Pete Sampras, when he experienced something similar. Note: I'm not comparing Petra to Pete Sampras. But they're similarities that can be drawn.
After Pete won his first major/The US Open, he admitted the following year there--he was "nervous" and didn't want to deal with the pressure as defending champion, and lost.
Needless to say, Jimmy Connors--who beat him, skewered Pete regarding his non-competitive comments and his wilting under the pressure. And for the next two years Pete had (admittingly), so so results; hadn't found himself on the court; didn't know what to make out of his tennis career, while a self described poor practice player at the time.
Guess what!? Eventually Pete changed coaches and found Tim Gullickson--who he clicked with, where he learned to practice better and harder, in addition to focus and refine his game under.
Two years later, after his infamous loss and comments, in defense of his US Open title, and his subsequent struggles after....Pete Sampras overcame his demons (and poor clay season leading up to it), and won Wimbledon. Needless to say: He won it 7/8 years, and picked up a few other Slams along the way.
And the rest was history (including his tenure with Paul Annacone, after Gullickson became sick and eventually died).
Sampras is not the first Grand Slam winner, with great potential to experience this (poor or up and down results, and lack of confidence and focus after their first major), then later mature and dominate. This goes for both sexes. So Hopefully, Petra will be the same.