Forgive me for stepping into the 20s thread, but I had to post and agree with those who think it's those weekends off that are creating the apparent stall.
It takes some people about a week just to lose the water weight they gain from eating a lot of sodium in one off-plan meal--let alone what two days of eating that way will do. She might be steadily losing fat, but unable to see it because she repeatedly regains and loses water weight each week. Alcohol exacerbates the water weight gain too.
During the week, she's really going low on calories. Depending on how she's eating on weekends, that could be a huge swing. For five days, she's training her body to be more metabolically efficient, then for two days she's keeping no tabs on her food intake. As Haley said, that's a good recipe for maintaining, not losing.
Maybe she could try a little more balance--still give herself some freedom on weekends and buckle down during weekdays, but keep the swings more modest. That'd mean at least a little accountability on the weekends too, but it's easy to fit a lot of good stuff into, say, 1800 calories on weekends and 1400 on weekdays (or whatever numbers she finds easy to live with that aren't as widely divergent as what she's currently doing).
I feel the pain of a plateau, as I'm kind of in one now. I hope she gets un-stuck from hers soon.