Fucking any horse will depend on the horse. Pet the animal, talk to it softly, spend time with it gaining it's trust. If something you are doing upsets it then don't force it. Talk to it and calm it. If you work slowly you can make an animal accept anything.
All animals fear man if raised in the wild.
How any animal reacts will depend on it's own experiences. When the filly reaches weaning age, seperate her from her dam. If you have limited time to spend then she should be put to pasture. If you have plenty of time then you should keep her in a stall. Spend time with her during the day petting and grooming her and allow her some time to run free.