Djul - well I hope you're right that she loved the game, only the game, even if nothing else to do with it
Seems pretty clear to me that she felt instantly liberated after she retired (although of course may have felt liberated from the apparatus of the game) - plus of course the whole unexpectedly falling madly in love improves anyone's mood
What I would reconstruct from various interviews is a trajectory something like this - quite different to Agassi if ending up at a similar point. She loved tennis as a kid and as a teenager ie moved up between the ranks very smoothly, everything came very easily etc.
1989 on - seachange. She definitely said this ie had loved it and ceased to love it as this time. Why? Already on the tour for years and fed up, probably burned out, feeling a lot of pressure, thinking of abandoning tennis for track (kind of wish she would have done that - would have been epic), growing up and starting to realize there might be more to life (in tandem with NY photographer boyfriend who was older, more a person of the world, lots of new adventures with him no doubt including the since lifelong interest in photography), lots of conflict with Slozil in part apparently over control issues re her offcourt life/boyfriend & fed no doubt by some on court losses. This was the phase of painting her bedroom black and spending days there if I recall. (Agassi also did this....) I would say she was probably actually depressed at this time. (And the parental drama on top of all that..)
1992ish - got her act together. Slozil out and Heinz in and much more accepting of her as a grown up with other interests as well as a better tennis coach (imho - I think he did a great job with her); steady boyfriend in Bartels who was more compatible with tennis than the NY guy; refocused on tennis as a fixed term commitment after which she could get on and have the life she wanted - that is she could see the end at the light of the tunnel and identify it as a short term deal worth doing as well as she possibly could; more secure about herself, appearance etc.
Heidi said later she really only grew up 1998 or so - long adolescence as Agassi again pointed out being common to many players due to nature of their existence.
1999 - a lot of rapid fire grown up decisions about what she wanted to do with her life. Bartels and tennis out; Agassi in. Off to the races....