Bonnie is a name that absolutely does not need a nickname. Nicknames came about for two reasons. One was that there would often be many people of the same name, if the name was popular, such as Elizabeth, Mary, or John, and nicknames were needed to distinguish one bearer of the name from another. The other was that some names are long, and tiresome to pronounce in full each time you use the person's name, such as Victoria or Alexandra. This doesn't mean that every name is required to have a nickname. I myself have never gone by a nickname because my name doesn't lend itself to them. Bonnie doesn't fall into either of the above two categories, and does not lend itself to nicknames.