Several sources seem to interpret the name Xiomara, which is now becoming fashionable with Hispanic parents in the USA, as a Spanish form of the Germanic name Guiomar. This site has that interpretation, though it does say "possibly".
I have just discovered, however, that there is a famous woman in history with the name who was not German. That is Chiomara, wife of the ancient Galatian leader Ortagion, who is the subject of a legend saying she was kidnapped and raped by a Roman centurion, and then tricked that centurion while she was being returned to her husband, and beheaded him, making the remark that she preferred to have only one man who had had intercourse with her alive at one time. Her story was first written in Greek, and the "Ch" of the spelling of her name in English was "X" in Greek, as shown by this article in the online Ancient Library:
The Galatians were the Celtic people who invaded and settled in what is now central Turkey. So wouldn't Xiomara be a Greek or Latin form of some Celtic name, and not Germanic at all? If so, are there any experts in Celtic languages on this board who could give a Celtic interpretation for Chiomara or Xiomara? The story about the original namebearer is so dramatic that I can easily see it being introduced into Latin America, or Spain itself, through some literary reference to her, instead of being an alteration of Guiomar.
Here is another online reference to the legend of Chiomara: