Oh no... I am so sorry for you.. Cough syrup is one of the most addictive drugs ever!! I have done all opiates and its sick to say that the syrup was my most enjoyable drug EVER. Also because of it I now have permanent heart problems and a sleep disorder thanks to it.
I moved on from it because it will kill you if she keeps abusing it. I have been in a methadone program at my VA and doing great now but would be hard for her to get into a medication assisted therapy which she most def will need if she is a chronic self medicator. She is obviously being tormented by some kind of trauma she needs to get out of there because her brain is going to be completely fried if she doesn't stop.
Its common and much more people like her are rising in america because newer addict's do not want to use street drug's and risk incarceration so they use dextromethorphan syrup and alcohol instead. Im sorry I cant help more but It would be hard as you need to be using a true opiate to get onto that or suboxone which can help her. She needs to see a phyciatrist but if she even refuses that find a way to commit her..