The most the Basal Metabolic Rate can vary is in humans of the same age weight and gender is 35 calories per day. Human bodies cannot defy the immutable laws of physics.
The most weight a sedentary women can maintain on 2000 calories per day is 140 pounds.
These numbers represent a woman who sleeps 24 hour per day
Resting (basal) metabolic rate: 1344 calories per day
Typical daily activities: 604 calories per day (sleeping is an activity) Chemical processes occur when we sleep and they require energy/calories
Total calories burned: 1949 per day
If she were even slightly active she would not even able to maintain 135 pounds. If she were moderately active 130 pounds is all she could maintain and if she did serious workouts 110 pounds is all she could maintain on 2000 calories per day.
Your BMR is approximately your current weight X 10. If you want a more accurate here is a free metabolic calculator http://www.stevenscreek.com/goodies/calories.shtml
If you eat at your BMR you will lose 1 pound per week per 100 pounds of body weight. That is IMO the most you can safely lose. Doctor may say other wise but again IMO many doctors are a menace who want to push junk like Medifast and weight loss surgery.
With the correct mind set and proper technique weight loss is not a chore. Marie Osmond is an example of that. Marie wen from fat and unhealthy to slender, health and sexy.