
Don't worry, she is showing all the signs of early labour. The nesting panting can start up to 48 hrs before labour begins. Some bitches still want to eat in early labour, one of mine always does then throws it all back up later, usually though they will stop eating when imminent. She may well want to be close to her owner now at all times, I would not leave her alone now.
regarding her due date, the due date really is only a guide for you, most bitches come on that date but depending on when she actually ovulated as sperm are viable for quite a number of days, this can put bitches past their due date.
I hope this helps. added to say go with Val's advice also if you are concerned about the bitch.