These are the original arms of Katherine Roet (before either of her marriages).
The coat of arms has three wheels on it since "roet" means "wheel" in
Flemish (the Roets came from Hainault, near Flanders). In heraldic terminology,
this coat of arms is described as Gules, three wheels Or.
The Roet coat of arms was apparently taken up by
Thomas Chaucer (since his father
Geoffrey married Katherine's sister
Philippa).
Here is a drawing of Katherine's tomb. She and her daughter Joan Beaufort
were both laid to rest here under a carved stone canopy (Lincoln Cathedral,
1403).