My sister was recently arrested for drug dealing, she was addict and to pay for her addiction she turned to dealing. The year before she was arrested my father told the police that she was involved with wrong people and we tried to help her but because she is over 18 we could not do anything. Instead of helping us they built case against her for about a year and then arrested her charging her with 15 criminal offences including felonies.
An attorney would have to take a detailed look at the case to determine if any rights were violated or if there are any defenses. The best thing you can do at this point is to secure a criminal defense attorney, as these are serious charges.
Your sister absolutely needs to consult with a defense attorney, preferably several, and hire the one she trusts the most to help sort this out. Courts in this area can react harshly in distribution cases, so every effort should be made to minimize the damage and avoid conviction - if possible. If she has not yet made bond, you and your family can meet with attorneys and some of us will go to the jail to speak with her so that we can give better advice on how to proceed.
With regard to whether any of your sister's rights were violated, it is too soon to tell. The police do not have an obligation to "help" if someone suggests they keep an eye out for trouble (in the form of the wrong friends). That does not mean they did their job correctly. An experienced criminal defense lawyer will be able to gather the necessary information as the case progresses and advise your sister appropriately.