Wow!
Sorry to hear that man.
Just FYI in the future if she happens to drop more joeys,i would put her and the baby gently (Wear Gloves!) in a seperate cage in a nice quiet room with only a sleeping blanket on the bottom of the cage with of course food and water for her.
Or remove the male from the enclosure and put him in a different cage.
This way there is less likly the chance of any mishaps and she can concentrate on just feeding the babe without being disturbed by the male or any human presence.
Obviously check on them from time to time.
Just giving friendly advice for you.
In any case that really sucks,but i am sure she will have more to come.