Congratulations on your baby girl!
Honestly, I think it's a bit ambitious to try to lose 36 lbs by Christmas. That's 4 lbs per week, that's a lot. Maybe aim for half that?
Definitely focus on your fluid intake. Calories have a lot to do with milk production but so does water intake. It takes liquid to make liquid!
If you were losing weight on 1400 calories I'd add 300-500 calories per day to that and see what happens. If you lose too fast then adjust upward, if you lose too slowly or gain a little then adjust downward. Definitely keep a close eye on your supply, but you shouldn't have any issues if you're eating good healthy food and getting enough fluids. Cutting the sugar out of my diet helped immensely this time around. Now I fill my calories with healthy, protein rich foods and I'm not hungry or experiencing that mid-day crash that sugar gave me.
I'm doing Weight Watchers and it's been awesome, their nursing mothers program is great. It's basically counting calories and it has been working well for me. The only days I have downswings in my supply are the ones I don't drink enough water.
I'm glad you're here! Feel free to join us on the weekly weigh in for breastfeeders thread if you'd like to.