For the given name MIRABELLE:
http://www.behindthename.com/php/view.php?name=mirabelle MIRABELLI looks Italian to me, so Italians should help here.
In French (and German) "mirabelle" is a small yellow plum, the etymology of which is uncertain. I looked it up in an online dictionary and it says, it is also Italian (mirabella), so this may be useful too.
The fruit may have its name from a French place-name. Or else from Greek "myrobálanos" which originally denotes the fruit of a certain aok tree (spice oak? maybe Pavlos knows) and later transfered to the yellow fruit.
Andy ;—)