Immunity to Parvo

I just read a couple threads where puppy's had got infected with the parvo virus. Someone had mentioned that older dogs can be carriers but it doesn't hurt them. I was wondering how that worked. My puppy also picked up the virus when she was about 3 months old. It was rough going for about a week. I spent day and night with her confined to the back porch. I force watered her with pedialite constantly, and she did make it through, thank God.
My question is does that mean my dog is now a carrier of the virus? Does that mean my dog is immune for life? Or, can she still pick up a new strain some day?

Cheers, susan...