Back in those days, to be named Bridget would have been a curse.
Bridget was the stereotypical name of a poor Irish maid...Agnes was extremely popular back then, and was esteemed by Protestants and Catholics alike. Although I think it was inappropriate and rude for the godmother to react towards Bridget in such a way, she was probably right for that time period.
Of course, now it would be better to be named Bridget than Agnes.