She may be Beatrice St Maur.

Michael Andrews-Reading has produced this research in May 2006:


Bearing in mind the assertion that John Wroth, MP d1375), son of the
Lord Mayor of that name, first married Beatrice St Maur, I came across
the IPM for Thomas Seymour, knight (usually now called Lord St Maur),
who died 1 AUgust 1358.  I had been looking for it in the PRO series,
but couldn't find it, so was happy that it caught my eye in the
Thoroton Society's series of Notts IPMs (Vol 1350-1436).  It is only an
extract, and apparently an imperfect one, but it sheds some potential
light nevertheless:

C/135/140/4 Thomas de Seymour: Joan (sic; a mis-print or mis-reading of
John?) Worthy (sic) is his next heir, aged 19 years.

This would give an approximate birthdate for John (?Joan) Worthy, child
of Thomas Seymour's sister, viz 1339.  This is, at least, not
inconsistent with a potential birthdate for John Wroth (d 1396), the
son of John (d 1375) and his first wife, as the former John's son and
heir was born circa 1366.
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