Who is Mairead Delaney from Under the Jolly Roger: Being an Account of the Further Nautical Adventures of Jacky Faber and what is their importance?

Mairead Delaney is Liam's daughter. She is about Jacky's age and stows away aboard the Emerald rather than facing marriage to a young man she doesn't love. She is adventurous and eventually agrees to live in London as the head of the Home for Little Wanderers Jacky sets up.