Be very careful what you tell anyone especially therapists and other "professionals". Their sole aim right now is to make sure you don't do any harm to others, anything else is an illusion to get you to let your guard down and encourage you to talk to them.

To begin with they'll act like they don't believe you partly because their training is aimed at male peodphiles who do abuse children and partly to test you, they want to see how genuine and how strong your attraction is. The more you talk the more you tell them.

Another thing is they may try is to get you to talk about specific girls. Do not admit to any fantasies about any actual LG, do not even mention any girls you know or even come into contact with. For their sake as much as yours.

Given your fantasies and the fact you are a girl I'm not sure exactly how they will react but no matter what they tell you are not thier primary concern. They want to "protect" kids and more importantly themselves, you are not as important to them as "protecting" other people and making sure they don't get sued.

My advice is to listen to your parents and tell the therapist as little as possible. Clearly you have friends and family who even if they don't understand what you are they at least accept you, telling a stranger everything about you is extremely risky. They will keep notes and records of conversations so do not say anything that you might regret later.