Oh ouch! I feel for her, I hope the Princess has an uneventful recovery. Princess Sirindhorn is very popular with the public, many stated it was a shame she couldn't have been the Monarch, but it could never have happened.
Succession to the Thai throne is by nomination by the preceding monarch or, failing that, the Crown Council. Earlier this century (I've forgotten the year, I'm sorry) Bhumibol had the Constitution changed to allow women to be nominated. Many observers thought that this was intended as a warning to the Crown Prince to tidy himself up or risk being replaced by Princess Sirindhorn who, as KarenI said, is widely venerated. Her Thai title, which is translated as Crown Princess, places her above her sisters and encourages people to equate her rank with that of her brother.
Many thought (hoped) that the King would change the succession as his health declined and some observers thought that the present King's delay in accepting his succession might have been caused by a behind-the-scenes power struggle between the supporters of the Crown Prince and Crown Princess.