Confused about a possible post-partum cat?

I am watching a pregnant cat for my friend. I got her on Monday and they said she was due any day. I noticed that she had a tiny bit of blood by her nethers but there was no more bleeding that day. Her nipples were super plump but I could tell that she had not been nursed on. She was super tiny and try as might I couldn't feel any kittens.
Today I was playing with her and I noticed that her nipples are now normal. No more pink and they are flat against her tummy. I've been checking her everyday and today she has a large amount of discharge that looks to me like lochia. She hasn't been out of our sight so I know she don't have any kittens at my house. Could she have had them before I got her and just now is having lochia discharge?
I've been fostering kittens for years but have never had a cat before the babies were Ben so I have no idea what to do or tell my friend.

seems  to be an enigma...

Everything is possible.  

The most probable, she had a  quick delivery somewhere - they can go literally in minutes sometimes,as  some of our forumists tells.  They were stillborn, perhaps a little premature, so she ate up them.  No traces save a little wet somewhere if you are very observant.

I have nothing to add to what Stefan says. Unfortunately the kittens are gone.  Most likely she did eat them. There is a small possibility you may find them hidden/buried somewhere at some point.

There is nothing to be done at this juncture. I am sorry you had to experience this and hope you will urge your friend to get her cat spayed immediately.