Thanks for posting your question. It's not uncommon to see them go for 48 hours or longer after giving birth. Keep in mind that the body normally evacuates feces prior to deliver and during delivery because of the straining.
You also have to keep in mind that she may be keeping her den clean by eating it.
My suggestion would be that you use a one inch strip of laxatone applied to her paw and let her lick it off. Or 2 tsp of canned pumpkin added to her meals. But it sounds like you're already doing that.
I would just keep a close eye on it and see your vet if you have concerns. But it's pretty normal.