Agnes de Courtenay

Thomas de Courtenay and Margaret Beaufort did have a daughter named Agnes. Alison Weir, in her work on British Royal Families, gives her as married to Richard Saunder. The dates for that Agnes, however, are problematic; in order for her to have married and had children when she did, she would have been born after Margaret Beaufort’s death, or at least after Margaret Beaufort was having children.

That profile can be found here:

https://www.geni.com/people/Agnes-N-N/600000000086231324