How long did the seizure occur before birthing? I find it strange that a vet would say it's eclampsia then just let the chin go home. The toxicity in the body is caused by the placenta generally and is only corrected by removing it, thus induction of labor or c-section. Not doing so puts the mother chin at risk of or organs failing. Dextrose is a sugar and wouldn't do anything really for eclampsia, and the calcium if hypecalcemia was an issue could stop the seizures, but that has nothing to do with eclampsia. Usually if eclampsia gets to the point of seizures it's because the body is on the verge of shutting down.
If it was truly the case I feel the vet acting wrongly, or if it was misdiagnosis, then again the vet was wrong. I know a doctor would never send a human home who had suffered a seizure from eclampsia, which is the proper term for toxicity due to pregnancy, toxemia itself refers to toxic state of blood, which can be caused by many factors such as kidneys failing, etc.
ETA: I agree with Claire, none of those meds would be used to treat true eclampsia, and this happened about 4 weeks before littering? If it was true eclampsia the mother would've died from toxicity well before those four weeks.