The fact that somebody breeds or has a large quantity of animals means nothing to me, considering the amount of people I've encountered that consider themselves ratteries or 'breeders'. This is not saying anything about crazy rat lady's competence, but rather that self medicating before first talking to a vet, or saying to seperate a pre-weanling rat from it's mother, is not what I would consider sound advice. Pedialyte is a good option if she will take it, but giving the implication that pedialyte and avocado is enough to cure a rat that potentially has a URI that will require antibiotics is irresponsible.
As mentioned by AK907, the 'treatments' mentioned above might be appropriate for a mild, or very start of a URI, but since the OP indicated that they are not sure how severe this issue is, I chose to give advice on gauging the seriousness of the issue, followed by a suggestion to head to the vet.. rather than suggestion for self-treatment and an implication for a successful recovery.
The problem with prey animals like rats, is that they are particularly good at concealing when they are ill in order to survive. It is therefore necessary to be very diligent when it comes to noticing, recognizing, and appropriately treating them when they do become sick.