I agree, how many people have we read about that had to give up their house because they couldn't afford it....and the D wasn't even their decision!!! I don't think it is your problem, if she wants the house she has to be able to afford it.
I had to get another job AND move...there is no way I could have afforded the house we were in with the job I had.
The only thing I think should be any concern to you is your D16's health care and D18's school.....but you ARE paying her 3K a month!! This was HER desicion...consequences my friend.
