I said this in the Federer and Murray thread but I really think Gaby's decline and eventual extinction as a serious contender at the very top of the womens game was in 3 phases:
-Losing the 91 Wimbledon final to Graf. This was step 1. Had she won this match she would have taken over the #1 ranking either right after or soon later that summer. She would have held 2 of the 4 slams (Seles also holding 2 plus the WTA Championships), and with her overall success in tier 1s she would have felt like a worthy #1. This would have done a huge amount for her confidence, and possibly given her a fighting chance of defending her U.S Open title too. As it was losing a big match to Graf yet again after serving for it twice, and after so many wins over Graf that year going in, was a damaging blow. After this she began minor decline, nothing drastic yet, but by early 92 she wasnt looking like a heir apparent to #1 anytime soon anymore, despite still being at #3.
-The 92 French Open semis to Seles. This one she lost after being up 4-2 in the 3rd set and it was the 2nd straight year she had beaten Seles in the Rome final but couldnt follow it up in the RG semis. This was a further setback, and apparently the loss that led to her split from Kirmayer. After this she began a more moderate decline, and by early 93 pre the RG fiasco she was already being bypassed by people like Sanchez and caught up by people like Martinez, Fernandez, and Novotna.
-The grandaddy of them, the 93 French Open quarterfinal to Fernandez. She had actually played pretty well this clay season, despite not winning a title, and had a good situation with Sanchez and Graf both off form at this event. This could have been the start of her recovery, but instead it was the death knall and the end of her ever being a serious contender for a slam title again. She admits in the years after she often drank herself to sleep on the tour, since she was mierable, and totally lost her enthusiasm to play tennis after this match.