Is it right for me to gain weight?

I'm a 16 year old girl, 5'10'' and 128 pounds. Yes I know I need to gain weight but is a pound a week too much? My nutionist says i need to eat 2500 calories a day and I think that is awefully high especailly when my mom is not allowing me to exercise. Will I gain some of this wieght is muscle? my mother says because I already have refined muscles a lot of the weight will go to helping them grow and not so much fat but I'm frightened. I know i have an eating disorder but its tough to force myself to gain weight. Do you think I will be ok with 1 pound a week and will some of the weight be in muscle?