I bet you could work those two goals at the same time, try to gain muscle and weight. You probably would want to increase over your maintenance calorie range by a couple hundred a day, but I'd say with more lean protein, and healthy, nutritious foods rather than empty calories.
I don't know what your exercise is like, but you should be doing some strenght training, to tone and incresae muscle, or lean body mass you may want to do this at least 3 times a week. If you use a lighter weight and more reps you will absolutely tone and shape your body, women have a really difficult time bulking up, even if they try really hard to do that.
highest weight ever:202, SP starting weight: 143
New goal: 125 lbs, just to see what that looks and feels like! Hit it: Feb 2013!
H: 5''4" 49 y.o.
"Don''t let yesterday use up too much of today." Will Rogers
"Eat Food, Not Too Much, Mostly Plants" Michael Pollan
| current weight: 10.4 over