Just tell this lady that she has no authority to baptize anyone unless he or she is in danger of death, and is likely to have wanted to be baptized (or the parents are likely to have wanted their child who is not yet seven years old to be baptized). The best thing for her is to wait to be asked to do the baptism, rather than taking any initiative of her own.
Also inform her that she must let the parish priest of the parents know that she has baptized that child, if she does so, so that if the child lives, he can complete the Rites for the child, and so that he doesn’t accidentally re-baptize the child at a later time, not knowing that the child has already been baptized.
Also tell her that she must under no circumstances ever - not even in danger of death - baptize the child of non-Christian parents. She could get into really serious trouble if she does this, and she could also get the entire Church into a public-relations nightmare that would seriously harm our Christian witness in the world for generations to come, as happened in the case of a housekeeper who baptized a Jewish baby when it seemed to her that he was in danger of death.
The baby lived, and because he had been baptized into the Christian faith, he could no longer be allowed to live with his Jewish parents, and he was taken away to be educated as a Christian. The Jewish people have not yet forgiven us for that one, and whenever anyone tries to discuss the Christian faith with Jewish people, that case is always brought up as an example of “forcing our faith” on to them. Yes, it was the action of a well-meaning but very stupid housekeeper - but the negative impact is world-wide, lasting, and deep.