English Latinate form of Isabel, popular since the 18th century.
A large number of spelling variations occur in the 1841 Census of Aberdeenshire. The most frequent are given here but all should be found using Soundex searching. However many of the abbreviated forms may not be found by Soundex.
Isabella is the most frequent of all the variants of Isabel/Isobel, Isabella/Isobella in the 1851 Census for Rathen; however in one case the name has been divided as "Isa Bella"; this may be an obvious alteration but it indicates the care needed when searching records for "composite names", or ones that can be so construed.
In old documents in Latin, Isabella will generally have been used, with appropriate case endings, for Isabel and its variants.