Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your little one has Parvo virus. Ideally these little ones are best treated in a hospital setting with intravenous fluids, and injectable medications to control nausea as well as injectable antibiotics. Unfortunately due to the effects of Parvo virus on the cells lining her intestinal tract digestion and absorption is very compromised, and secondary sepsis due to gut bacteria gaining access to the blood stream via her raw intestinal tract lining is often the cause of death.
I understand that financially this isn't always possible. In those cases we can try administering subcutaneous fluids, using oral antinausea drugs and antibiotics, and forcing oral fluids as we can, but being careful not to overdo and cause further nausea.
The short answer is that yes, her body should eventually absorb the dextrose solution.
But we don't use fluids containing Dextrose subcutaneously because they are highly irritating and can lead to tissue death and the loss of overlying skin. The other concern is that fluids with dextrose in them are much more likely to harbor bacteria in them if not handled asceptically and thus the chance for secondary infections are greatly increased. Depending upon the concentration of the dextrose solution she was given a one time dose may not be harmful. 5% dextrose isn't nearly as tissue toxic as 50% dextrose. My hope is that the fluids given previously will dilute out the dextrose that you administered.
I would not administer any more subcutaneous fluids of any type until all of the fluids are absorbed, and I would not give any more fluids near the site where the dextrose was given. That tissue is very fragile now.
I would not administer expired fluids, nor any more fluids with dextrose. For now I would try oral fluids only given our concerns about being given dextrose subcutaneously.
I don't expect her to feel like eating.
But as long as she isn't vomiting you can make a gruel of canned puppy food and pedialyte in the blender and give her a few tablespoons with a medicine syringe every couple of hours. If she handles that well slowly increase the amount at each feeding.
If she begins vomiting again, the area where the fluids were given becomes raw or begins to ooze or feels hard/stiff she should see a veterinarian promptly.
Best of luck to you and Brownie.