Cresties tend to be pretty resilient, so my instinct would be to leave her alone for a few days and see how she does. Moving her to a quarantine tank was a great first step. If you have Neosporin or another triple antibiotic-- no painkillers!!-- you can use that on the wound for the first four or five days to keep it covered and moist and help prevent infection.
Mine have gotten various scratches and nicks, mostly from encounters with the cats, and this has helped them out. That said, I've never seen anything quite like that with my gex. If someone more experienced with this kind of injury chimes in, I'd go with their word over mine.
Good luck!
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