I'm with Jupiters in that I feel like hiding alcohol is a gigantic waving red flag because I have never, ever known a normal drinker to hide alcohol. Ever, ever, ever.
But EVERY alcoholic I know HAS hidden it, in so many ways it astonishes me.
The brother idea may help depending on their relationship. It's possible she'll feel attacked and defensive no matter who tries to deliver the message.
It is definitely something she has to decide for herself to fix about her life, but in the meantime you can stay on your side of the street & not get sucked further into the spiral. I hope you take some time to read the sticky'd threads at the top of this forum. They contain ages of wisdom & experiences about all of this.