It's quite possible the teacher found it.
I don't know if this is a good thing or bad thing -- basically it ticked me off that I knew the teacher had *lied* the entire time even though it worked to my benefit.
In 8th grade Science we had a folder due and it was a huge assignment, we were told at the beginning if we didn't turn in the folder on the day it was due, no excuses whatsoever, you get a zero.
Guess who left the folder sitting on the kitchen table the day it was due? I never bothered talking to the teacher about it, thought Oh crud, oh well, he said you would get a zero & there would be no excuses whatsoever so no point in telling him I forgot it at home. I knew I was getting a 0 and it was, what it was.
Fast forward a few weeks later and he asks to see me after class around the end of the marking period. He asks me why I didn't turn in the folder, I told him I had forgotten it at home on the due date & he wanted to know why I didn't let him know about it as he would have let me turn it in late. He also wanted to know if there had been someone to call & I could have turned it in at the end of the day (i.e. after class was over, so I would figure that would be considered late)

I think I had deer in headlight look thinking -- WAIT..you TOLD us that you would not accept it late whatsoever & no excuses it was a zero, so why in the world would I tell you on the day it's due that I forgot it at home. I figured there was no point in doing that, it wasn't as if you were going to accept it then. I didn't have the guts to actually SAY that to him (I think I was annoyed because he seemed mad at me that I didn't even bother to tell him -- well DUH, why would I?). He just told me to bring the folder in the next day and he would grade it. He gave me a C on it knocked down from a B for being late.
Apparently, he his speech wasn't for the kids that actually did their work on time 99% of the time and messed up once but being a kid myself & hearing VERY clearly those directions, I didn't know it didn't apply to me.
So, I would definitely have your daughter talk to her teacher. If it's an unusual circumstance, she may give her extra time or some way to make it up.