Of course you didn't know.. most people don't and don't see any problems at all with putting their pets with their friends pets to make cute pups
The reason why it's not a good idea is because you don't know the proper full lineage and if there are previous health problems on either side. They can't be registered so anyone who buys your pups that wants to breed can't trace anything back either.. then we have a whole line of JRT's that are un registered and no-one knows for sure if they are really even pure.. because there is no proof.. no papers no proof.
The health testing etc is very expensive and registered breeders are very serious about what they do and don't take kindly to people ruining their hard work to make cute pups
Anyway, welcome to the forum.. I hope you take Molly under your wing and learn some stuff to teach to your family. She needs someone special to look after her and I think you are the one