caught coworker drinking on the job

I work at a salon and I caught my coworker with liquor in her cup. She doesn’t know that I know. I saw her cup in the breakroom after she left one day and figured I’d just wash it to get it off the counter and ready for her the next time she came in. When I poured (what I thought was water) out i got a strong whiff of vodka. The next day I saw her with the cup, I was alone in the breakroom again and lo and behold it was vodka again. Today it was wine. She still doesn’t know that I know she’s drinking while working.She’s an amazing stylist and we’ve also gotten super close since she’s started. I absolutely do not want her to get fired. How can I help her? 😭