Some comments by Two-hander and the comment on the WTA site that one of the other woman players made got me thinking about this. What she said--and I've forgotten who it was--was that if she could have any attribute of another player, she would have Safina's fighting spirit. This struck me as a strange choice, but then I began to remember a lot of matches where Safina did struggle to eke out wins.
So...what is a headcase anyway? I think there are several definitions:
1) A player who fails to live up to their talent
This definitely doesn't apply to Safina. Safina's talent is that she can hit a pretty big ball off both sides with some topspin for safety, which isn't common in women's tennis right now. Her serve, despite her height, wasn't a huge weapon, even before she got the yips this summer--it wasn't a weakness, but it wasn't that special. Her movement on hard courts is clearly worse than any other top player today, and that's a huge liability. The only top player recently who moved as poorly is Davenport, and Davenport had a better first strike (serve & return) that enabled her to avoid being on defense more often, as does Sharapova. Honestly, I'd say Safina is clearly not only less talented than Sharapova, but less talented than Kuznetsova, Dementieva or Petrova. It's actually surprising that she's had as much success on hard courts as she has. Because she trained in Spain, clay helps her movement and her groundstrokes have more margin for error than the flatter hitters, so her talents are better suited for that surface....but I still wouldn't rate her skills as better than Kuznetsova's for clay.
2) A player who habitually loses leads and struggles in close matches.
While she's lost some, she actually has a record of fighting through tight matches pretty well. Just in 2009, she had narrow wins over Cornet, Dokic and Zvonareva in Australia this year, over Jie Zheng and Venus in Rome, over Safarova in Madrid, Azarenka at the French, Mauresmo and Lisicki at Wimbledon, Errani at Portoroz, Vinci in Cincinatti. Yes, she's lost a few too, but her record in tight matches is probably better than most players.
3) A player who can't win on the big stage.
This is true, but only partly. Note above that there were matches where she fought hard to eke out toiugh wins against decent opponents at all three majors this year. She finally lost in the 3rd round here, but her form was so far below par, she was fighting to stay in every match she played. Against that is a small number of catastrophes at or near the finish line in the slams--against Ivanovic at the French, against Serena in Australia, against Kuznetsova at the French, and against Venus in Wimbledon. But with the possible exception of Ivanovic, all of those are players that--from an objective evaluations of her tennis skills vs. theirs--she should lose to.
So yes she has caved in on the big stage, but only against players of superior skill. And yes, she fell apart mentally and got ripped to shreds in those matches. But that's happened to another poor mover in a couple of big matches as well (Sharapova). Sharapova has counterbalanced that with a few big wins and has a reputation as a figher as a result, but like Safina, when her first strike fails and she's forced to defend a lot, it can get ugly. And Safina's first strike is not as deadly, so...she's more vulnerable to having this happen.
So on balance, while she might not rank as the mentally toughest in the game, she's certainly not a headcase in the league of Petrova, who fits all three of the descriptions above.