
As you say 24/7 supervision, use wet wipes to help with toileting.
Have her Calcium levels been checked as the kind of behaviour you describe can be a sign of Eclampsia.
Also is her whelping box den like or open, she may be feeling her pups are not safe and secure if it is too open. Was the loss of the other two pups traumatic for her (were they distressed, several days old or lsot at birth?)
Is she able to hear any other dogs, which can make her want to hide them.
Otherwise sit quietly by her, put pups on the milk bar (the act of them suckling should relax her) and praise her quietly for being a clever girl.
Things will improve once pups eyes are open and they can see what's what and get out of Mums way.