A fascinating name! When you Google it, almost all the references are on geneology sites, and, just looking at the first four pages, the earliest one is Anstris Palfrey, who was born in Salem, Massachusetts way back in 1691:http://freepages.books.rootsweb.com/~rbrown/salem/birth-38.htm
Anstice was a medieval English form of Anastasia
. I suppose there's some chance that Anstris is a variation of that -- but I don't know how on earth the "r" got into the name if that's the case! Hope
someone else has some more information.