Blaes of Matuchin is a character in the ballad, The Bargain of Rogosh Eagle-eye, performed by Thom Merrilin in the common room of The Stag and Lion in Baerlon to honor past Heroes of the Horn. There is no information on whether she is fictitious or a real historical figure.
The prose of the ballad portrays her thusly: "strong as the ash she stands, as lithe as the willow's branch, and as beautiful as a rose. Golden-haired Blaes."
The ballad makes it clear that she is either royalty or high nobility as she has heralds and a court, the context infers something similar to a royal court.
During the Last Battle, the Horn was sounded again, this time by Olver, a feat possible due to Mat's "death" at the hands of Rahvin in Caemlyn. Blaes was summoned once again, and among other things, informed Mat of the powerful yet vulnerable nature of the Heroes.
—Blaes of Matuchin
Mat considers her very pretty.