Actually, the description of the 16 year old girl the writer gives makes me think that she probably has severe ADHD. Her behaviors are not unlike that of my teenager, who also has ADHD, when not properly medicated. Such as, speed reading one book after another and letting practically everything else fall by the wayside, the lack of attention to personal hygiene, the absence of the knowledge of details to take care of herself and achieve what seems like simple goals, and the terrible grades. Females often remain undiagnosed well into adulthood, if ever at all, because they usually do not display the "hyperactive" behavior than most people think is required for ADHD. Rather, girls are described as absent minded, staring out the window daydreaming, easily forgetful, unable to complete tasks that require multiple steps, "absent minded-professor". I would advise the letter writer to invest just a little more in this girl before abandoning her to a father who obviously has no clue. First, just google "adhd in girls" and see if that doesn't bear an uncanny resemblance to what you are dealing with. Then, talk to her teachers at school and get them to write letters describing the behaviors and problems with the school work, then get yourself and this girl to the nearest pediatrician and lay it on the line by telling the doc what you have seen from her in her homelife. Any pediatrician can prescribe the necessary meds to control adhd, and soon you may find that she has become so much more manageable. If you get her the help she needs, she will like herself more, and you will like her more and from there you can start to build a decent relationship with her. The longer she goes undiagnosed and untreated, the harder this life will be for her. I think you have been given an opportunity to change a life and you will be made a better person for it.

The author of this letter seems to be displaying traits of bipolar disorder and will only be able to get help if she/he seeks medical help through either a medical doctor, or more specifically, a psychiatrist. None of this other advice will do any good until this person receives proper medical treatment for this disease.