Dane litters average around 6-10 pups so it sounds like she has quite a few in there!
It would be just like a pregnant human, the last few stages would be very uncomfortable.
Danes having a litter is no different to any other breed except for the expense and the size...
Does your whelping box have rails fitted inside it? This is very important with large breeds.
You need to fix either rails or just wide strips of wood inside the box a few inches above the bottom so that when the b*tch lays down any puppies underneath her get pushed against the wall underneath the rail, hopefully saving them from being squished.
As for the whelping, well there are too many thing to list here so I will have to provide you with a link to read.
I love this site by Chelsea Collies, it details what you will need when whelping pups as well as care after they are born
Newborn Puppies....Care of the Newborn puppy
One thing I will say is to please get your b*tch spayed after this litter, Great Danes are extremely hard dogs to grow and I have seen far too many people buy puppies and ruin them simply because they do not know what to feed or how to care for them properly as the 'breeder' does not give out care sheets.
If you would like help on writing care sheets for great danes please let me know (My mother has been breeding them for 20+ years)