Two of my snakes escaped very recently and I found them both in about a week. I had a lot of good suggestions, but they hadn't been gone that long, and I don't know if its different since shes been gone for like 8 weeks.
Since the little girls been gone for so long and used to being regularly fed, she may be hungry. When my snakes escaped, I put little ventilated cages around the house with mice in them and layed flour down around the cages, in door ways, along walls, or other places I thought they may be crawling about. The flour worked like a charm and helped me track them down. Its easy to sweep and vaccum up and not harmful to the snakes. Another good suggestion I was given was to get plastic bags and crumple them up behind couches and in corners. They're quiet (obviously) and that can help so you can hear her slide through it if she's in the area.
Check places you wouldn't think shed be. Like in book cases (someone once told me they found their 4 foot ball in a 2-inch, 2 ring, binder in the bookshelf), in the mechanics of the washer and dryer, around the hot water heater for warmth, and behind the stove, on top of cabinets, etc...
Good luck to your friend.