Actually, we give incompletes at this stage of the game (though personally I think it should be an F that wouldn't sit well with the more senior faculty). With an F, you are automatically kicked out of the program. Incompletes turn to F's within a year and then you are kicked out.
If you give her an incomplete, she will automatically have a clock ticking down to the time she is automatically kicked out of the program. What's nice about this is that it becomes clear that it's HER ticking clock, not yours. So lay out the timeline for her: "In order to have that incomplete not turn into an F, automatically dropping you from the program, you need to have X done by Z date. In order to get X done by Z date, you will need to have done R, S, and Q by Y date." ... etc.
It makes it clear that doing that work is her responsibility, not yours, and that she needs to take matters into her own hands.
I had to have a few conversations like this with doctoral students. They weren't pleasant, but they were necessary.
VP