My puppy is staying at the vet for one day?

Hello everyone, I have a problem, my 4 month puppy was feeling sick since thursday night, so next day I went to the vet early in the morning. The vet said that she has parvo, so she is in a treatment for 4 days. When I took her today for her shot the vet told me that she has responded to the medicine, but is weak because she does not want to eat, I have to give her gerber, and chicken sup. The vet told me that she needs blood serum because that will help her on the eating part, he says that she already passed the first 3 most difficult days, she has been sick for 4 days now. So she is staying at the vet for all of today. I am really worried, to me she is like my baby, I am used to living with animals and I always take care of them. It is just that I am worried, I know that the vet will do the right thing but I am too worried, I could not sleep at nights just to take good care of her, have you ever left your pet at the vet for one day?????.... I am just worried, she is part of my family... thank you so much, and have a great day.