I don't have direct experience of your situation, just a suggestion where to look for advice. Your DD may not be classic ADHD, but it sounds like she has real challenges with executive function, which is where so many ADHD folk suffer. From all that I have read, lying and ADHD very commonly go hand in hand as kids build up defences against their failures. It seems to be the go-to coping strategy. Lying around un-submitted homework usually tops the list. Most suggestions I've seen are around making clear the lying is unacceptable and has consequences, but focusing mostly on support and remediation of the deficits, as opposed to punishment.
So a google of "ADHD and lying" might be helpful. I went to
http://www.additudemag.com , my common starting spot, plugged "lying" into the search, and got 10 pages of links. Not necessarily deep info, but a good orientation before you dig in.
Hugs to you. I know this kind of behaviour is a huge, huge challenge for parents. Mine are more about always shifting the blame for any problem situation to others (a more indirect kind of lying), but it generates that same sense of failure as parents. Lying pushes all our buttons and is really, really hard to deal with calmly. DS and I have probably had the same fight 50 times since he was 2, and I'm still struggling to find a way to deal with the blame-shifting more constructively. I think we're starting to make a little progress - but this is clearly why I am pointing you to websites and not anything I've done.
