First off, you need to see a doctor and/or nutritionist ASAP. If any advice I give is different from them, go with them. They will help you better than Yahoo Answers.
Next, I'm a bodybuilder. I'm very amateur, but I still know how to gain healthy weight.
I'd also recommend doing a Google search on Pauline Nordin. She's a female bodybuilder. She doesn't look like a male, like you see the bigger Mrs. Olympia girls. She looks like a pretty woman with muscle. The reason I mention her is because she used to have an eating disorder as well. Eventually she took her obsession with how she looks and turned it into a positive.
You don't have to be a bodybuilder yourself someday to do the same. But with proper research on how to make your body healthy (which you are beginning to do right now), you too can turn your drive into a positive direction.
To figure out how many calories you need to gain healthy weight, I'd recommend finding out the maintenance level of calories required for your desired end weight. From there, add 500. I'm betting that will be under 3,000 calories for you, and it might even be less than 2,500.
See my source for a calorie calculator. This is not normally used for someone recovering from an eating disorder. That's why when you enter you information into the calculator, I suggest entering your desired weight, not your current weight.
I'm not sure if you can make it to 80 pounds by November. But you can keep going after November. Setting that month as your make it or break it time may be a bad approach. Just focus on a week to week progress until you get to a healthy weight.
Your food sources should probably stick to healthy things. You'll still gain weight if your calories are in a surplus. (Healthier food makes for healthier weight gain.)
Carbs: Oatmeal, brown rice, sweet potato, and just about all vegetables
Protein: Lean meats, eggs (especially egg whites), and protein powders
Fats (in moderation): Almonds (great snack, btw), olive oil, flax seed oil, peanut butter. (Adding more peanut butter is great for adding calories!)
The owner of the site of the calorie calculator I gave you is named Lee Hayward. He is a great person to talk to as well. You can email him, or join his message board (I'm Cylith there) with questions. We at the message board love helping people with diet questions. If you're too shy to see a doctor, at least try to get in touch with Lee Hayward.