Mary Caswell Washbourne is, I believe, correctly positioned here. The evidence to support her connection at this point is that her brother John also visited Yatesbury and had a son here. The Washbournes did not usually inhabit this village, but came from further north in the Malmesbury area.
Mary was probably born out of wedlock, and hence carried her mothers last name.
Her 'brother' was born before the parents were married.
So far the only record of her is her marriage to John Walter in Yatesbury on 31 May 1781.

I may have gotten this wrong here, but the connection is VERY valid . The
Washbournes, Caswells and Yatesbury were all connected at this time , and so the overall theme is correct.

But, since looking at her marriage entry in the Yatesbury register, and seeing that Robert Caswell was a witness along with Thomas Washbourn, we can be sure that this entry is correct. The curator was Thomas Greenwood.