Lots of "traditional" English names have nicknames and shorts that are somewhat puzzling, but they probably came about because the names were so common that variations were used to differentiate all the Marys, Annes, Catherines and such.
Thus we get Margaret- Meg- Peg; Mary- Molly- Polly; Anne- Nan- Nancy; Edward- Ed- Ted; Christopher- Kester- Kit and lots more. Many are surprise that "Polly" comes from "Mary", but it does! Name origins are are fascinating things!
Another name that surprises people is that "Daisy" can come from "Margaret"! Margaret in French is" Marguerite", which is a large kind of daisy. It was often given as a nickname in families with lots of Margarets. Of course it is also a flower name in its own right, but still- interesting.