Welcome Jenefer!
Definite yes on protein, flax oil, and food food food. No one cannot build muscle without it, especially someone like you who is already at a low bodyweight.
Your "ladies only" gym worries me a little. Do NOT be brainwashed by anyone telling you that ladies should train any differently from men. Train for STRENGTH, and all the aesthetic stuff will fall into place. Concentrate the most on weights and diet, but don't completely neglect your cardio training. Your heart is a muscle too, plus it will give you some extra energy.
Two excellent books I'd recommend are:
Bodyfitness for Women - awesome motivational pictures, lots of training routines from beginner to advanced, nutrition and supplement advice, even information on fitness and bodybuilding competition.
Serious Strength Training by Tudor Bompa - advocates "periodization" training which means cycling the emphasis of your training routines between muscle growth, strength/power, and muscle definition. Sample routines for beginner, intermediate, recreational bodybuilder and pro bodybuilder. Excellent diet advice and pictures of all exercises.