In the Yatesbury Parish records there is a Mary Chilcester who was
baptised 14 Nov 1622, no parents were mentioned. I think this is our Mary
as there is a possibility this was an adult baptism, as there were no
parents present.

The link to Mary Silvester in Wantage is tenious, but it is the only Mary (Marie) I can find searched Ancestry and familysearch.

However, Wantage is very close to Witney, and we know the sheepherding Caswell family was likely a regular at the Witney market, buying sheep and selling wool.
It looks like the Chilfester family of Wantage was fairly affluent looking at a couple of wills there.

Ancestry says Marie was from Cannings.
FHL Film Number:
1279349
Reference ID:
2:QQZR1L