The name translates as "White Breast". Being that it is an old name, coming from a time when the essence of beauty was the swell of a woman's breast, and the fairer the skin, the more beautiful; you might translate it in today's language as "Fair Beauty".
Just a side note- The name Bronwen; Bronwyn can be for either a boy or a girl. The spelling indicates which gender the bearer is. The -wen spelling indicates a female, and -wyn indicates a male.
Bronwen was a strong beautiful woman, with great poise and elegance.