Who is Mary Barr from Gandhi, the Man and what is their importance?

Mary Barr was an English woman to whom Gandhi wrote a letter explaining that he would remain loyal to the British empire if he must, but that he would continue to advocate for the rights of the poor, who are the most injured by the domination of the English. Barr also wrote a letter to Gandhi apologizing for disturbing his solitude to which Gandhi replied graciously that there was no offence: his solitude was always taken in the presence of many.