Hmmm... heartworm pills deworm once a month...
I don't think this is an emergency for you to rush to the vet tonight.
I would allow her water tonight, but not food, and bring her to your vet tomorrow to have a fecal check and make sure there is not another parasite (precipitated by the stress of pregnancy) or bacterial problem.
With a pregnant dog, you need to keep close tabs, which you are!!
I am a veterinarian that wants to give you an honest answer. If I helped you or your pet, please ACCEPT my answer. Thank you!