I suggest putting your fairies heal on a hot key or bind it to your mouse (if you have extra keys on it) She'll only heal when they dip below 70-75% (something around there) Which might not be ideal at all times.
I like to focus the tank and use my fairy to patch up any scratches my teammates incur, and vice versa. Its extremely important you learn to control her the best you can, she heals for quite a lot!