While I agree that in sports, it's not about winning, Serena was not feeling well since the start of the match and it was due to this that she abandoned the match. She did what she thought was right and I think it was right as well for one should put his/her health first and then everything else later for a fit person is able while an ill person only proves to be a liability.
I agree with her decision to stop the doubles match with her sister. Clearly she was very ill and she needed to be seen by a doctor immediately. If her illness was effecting her in that was there was no way that she was going to be able to continue to play anyways. At least no well enough to win.
It was clear that something was wrong with Serena Williams the moment she started warming up for her Wimbledon doubles match overnight.
She appeared to be disoriented, weakly pushing volleys into the net from a metre away, missing practise strokes and failing to pick up tennis balls that bounced her way.
When the warm-up ended, Williams was examined in her seat by medical staff, who checked her blood pressure. The delay was so long that one of her opponents, Kristina Barrois, asked the umpire whether she could warm up again.
Serena was obviously in some kind of medical distress, and her health is far more important than a game. Their opponents would have gained no satisfaction from beating a team that was so obviously struggling, and it was best to end the game before something serious happened. Finishing the match would have just been painful to watch.