McDonnell's early life was spent in Dublin, but then the family moved to Cushendall, County Antrim around 1885.
It is possible that McDonnell was the "cultured lady from Cushendall and trained in nursing" who took up the position as the first matron of Coleraine Cottage Hospital.
[1][2] McDonnell founded a toy factory in Cushendall in 1900, employing local people and promoting wood working skills.
The toys proved popular, and were sold in Ireland as well as England and the United States after they were exhibited at 1904 the St Louis World's Fair.
[1] McDonnell was unanimously chosen as the president of the first Glens of Antrim Feis in the summer of 1904, as she had a particular interest in the Irish language and other traditions.