Re: significators and indicators of addiction or drugs in horary
I'd think the best indicator for it using the planets found in classical astrology would be something to do with Mars, especially for alcohol. Obviously though since you mentioned it in your post you figured this as well.
However, if you don't mind using the outers I feel like Neptune would be a perfect fit (drugs, alcohol, escapism as a whole). I feel like since in this question it would be useful, as you'd already be using the 7th house ruler as her significator.
Personally I'd check Mars, Neptune, her 1st house (speculation on health concerns), her 6th house ( more definite health concerns/ sickness.), the 12th (drugs, alcohol, all the good stuff).