Isabella's surname

Various published or public family trees across various sites (including genesreunited, ancestry.com, familysearch) list her surname as Gunstone. Yet www.royalblood.co.uk indicates that Isabella's surname was de Longbrook
(http://www.royalblood.co.uk/D163/I163554.html). Familysearch.org also has her listed as de Longbrook.

The Visitations of the County of Cornwall JL Vivian, 1887 (http://www.uk-genealogy.org.uk/england/Cornwall/visitations/imgs/p6... ) indicates she is the daughter of ... Gunstone of Shilstow. Does anyone have any other sources for either option?