I have had this problem before with a bitch... I have found that giving my bitch Oral Cal Plus solved this problem for me...My bitch was able to care for her pups and keep her Calcium levels at a normal level...I buy the Oral Cal Plus from Revival Animal Health, the link below...
Oral Cal Plus
I give this every night before bed to my bitch until they wean their pups...You do NOT want to miss a dose...I would recommend taking her back in a couple of days after you start to have her calcium levels checked to make sure they are staying where they need to be....
Eclampsia is life threatening and not something to take lightly...Your bitch can die from this and I doubt that calcium pills will be enough to keep her calcium up considering the demand that 6 pups will put on her...
If you leave her alone all day while you are away at work I would suggest having someone that you can trust that will know the symptoms of eclampsia to check in on her...
Hope she does well...Good Luck!