Gunngifu is a postulated Anglo-Scandinavian hybrid female personal name formed from the very common Old Norse element Gunn- from gunnr, guðr ‘battle’ combined with the Old English element gifu ‘gift’.
There is a possible attestation of the name in a medieval document from Lincolnshire.
Gillian Fellows Jensen, Scandinavian Personal Names in Lincolnshire and Yorkshire. Copenhagen: Akademisk Forlag (1968), pp. 114, 344.