That is (cautiously) very, very good news! She contracted the virus at some point and will always have the antibodies, just like you keep antibodies for chicken pox or measles after the virus has gone. She likely cleared the virus on her own. Go back for the other PCR and then put this whole mess back to bed again and move on.
Yes, this is possible. The first test may have just tested for antibodies. That would have shown if she had ever been exposed. Once you have been exposed, you will always test positive for the antibodies.
Once someone has a positive antibody test, they will test further with the PCR you mentioned above. This detects the level of virus in the blood.
If the PCR came back with a number.....anywhere from 10 (depending on which test) to maybe up into the millions......that would mean she has the virus.-and possibly require further treatment.
In approximately 20% of patients that are exposed, their own immune system is able to kill the virus on its own., requiring no further treatment. It woulld appear your daughter is one of those lucky ones.
That's a great thing.