As someone who isn't too
far out of the teens, I'll tell you right now that saying something like "Would your boss give you extra days..." won't work. Work/adult life is "far away" to a teen.
As a teacher, I'll give another piece of advice: Find out why
your daughter didn't hand in the project. I don't mean her fake reason of "I forgot it at home," but really sit down and ask her if she was afraid to complete it or embarrassed that it wouldn't be good enough. Some children are so afraid of failing to do something that they restrain from doing it altogether.
I know your daughter is 16, but it might be time to pull in the reins a bit and work with her teachers. Let them know that you want to be involved (any good teacher won't mind this) and that you want your daughter to succeed. Ask the teachers how she is in class. Does she pay attention? Does she ask questions? Is she well-behaved? Ask the teachers what you can do to make sure she does her work at home, I'm sure you'd get some wonderful advice and because you're showing that you genuinely want your daughter to succeed gets you on the teacher's side and is overwhelmingly good for your daughter.
Find out major assignments/projects/tests and make sure your daughter completes them. Ensure that she writes her homework in a planner and check it. Question any blank spaces and if you don't care for the answer she gives you, question further.
I know a 16 year old's homework can be difficult to help with, but offer to. If she needs extra help, get it for her.
Her father needs to be in one this too, but if he isn't, you might have to pick up the slack. I've worked with children where their mothers would routinely call when the child was at the father's just to make sure the child was doing his or her homework (and the smart ones asked them questions they only knew they could answer if they did it!)
She'll probably hate all of that, but she can "earn" looser restrictions if she shows an improvement.
What are your daughter's plans for the future? If she plans on going to college and wants to go away, make sure to show her that she CAN'T do that unless she gets higher grades.
I know it's frustrating to have a child you KNOW is capable of doing something and they just won't do it. I wish you and your daughter success