The traditional yardstick in these types of scenarios is "the letter of the law versus the spirit of the law".
Of course she broke the letter of the law by wearing a bracelet and therefore is eligible for disqualification.
I do not know the original intention of this rule, but I would imagine that the rule is to prevent athletes from causing distraction with outrageous clothing and jewelry. It could also be used to prevent athletes from wearing watches to get an advantage or wearing jewelry that may cause an injury to themselves or others.
Since a rope bracelet is not going to cause distraction, potential injury or give an unfair advantage, I think that the spirit of the rule was not violated.
Just like driving 59 mph in a 55 mph zone may get you a warning, this girl should have received a warning for not following the letter, but staying within the spirit of sportmanship.