Isabinda seems to have been a name created by a playwright. The earliest instance I can discover is for the character Isabinda in
Susanna Centlivre's play
The Busie Body (the title often gets rewritten with the modern spelling
The Busybody today.) This play was written in 1709; it's a comedy, and the father of the character Isabinda, Sir Jealous Traffick, is said to be a great admirer of "Spanish customs." Given her father's name, I don't think the name of the character Isabinda is to be taken seriously. It is probably a deliberate alteration of
Isabella by Ms. Centlivre, blending that Spanish name with the ending -inda, which was extremely popular with poets and playwrights in England at the time when they were creating exotic names for female characters.
Melinda is an example of such a name, with
Araminta being a similar creation of that time period. Though most people have forgotten it today,
The Busie Body was an extremely popular play back in the 18th century, and Isabinda probably got into your family when an ancestor saw the play (or read it) and decided that Isabinda would be a good name for a daughter.
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