Hello,
I can give a bit more info about the issue.
I also encountered such a companion after the 'missing daughter quest'. She was the daughter and after i returned her back i thought i could buy her and form her as i'd like and need her.
But unfortunately i had no chance because as stated above, she has a skill of -204/5 to get to level 2 and has 0 attribute and focuspoints. Somehow she get magically 6 points by following me
. But that wont be enought to get to the next level. The problem is, that without any attribute or focuspoints, she will be unable to get level points and therefore is completly useless.
After that i paid attention and the same thing happend when i did the same quest again.
To solve the problem, she should get 1 attribute point in every categorie (the main caracter gets 2 attribute points in every categorie when we create him) and 2 free skillpoints after finishing the quest, because i like the idea of a companion that i can level from the begining. Also it would make sense, beacuse she is 18 and hasn't specialized like older companions. When completing the quest you have the option to tell the father, that she will stay with you, which will not make any sense if you cannot use her. But in regards to my solution her price should rise up, beacuse you get around 1500 for completing the quest and then can buy her for 700 denars, which wont make sense eather. Gues 2000-2500 for a companion that u can form as you need him is a fair price or u choose the option to keep her in your party, for a relation loss.