Ocassionally an ISA will go broody and will make a good mum although it is not common. ISA has also become somewhat of a generic name for brown X breeds. so it is possible that she is carrying some 'broody breed'.
In order to break her broodiness you need to remove any thing closely resembling a nest and put her in an environment where her belly remains cool - this will switch off the broody hormones.
There are lots of threads on 'Sin Bins' and breaking broodiness - click on the Search button at the top of the page. The basic requirement is a well ventilated, weather proof cage - raised off the ground (on a bread crate). Food and water, no nesting materials and a bit of space for exercise. If possible, a perch.
It takes about as long to break initial broodiness, as a hen has been broody. In the case of your hen, I would give her at least a week, or until she has been perching for a few nights, then put her back with the others. If necessary, put her back and try again.
There may be some initial aggression from the flock when she returns as she will be seen as a newbie - ISA are notorious for not being very welcoming. Keep an eye on her safety but try to allow the pecking order to sort it self out naturally. Ask for some help if there is trouble.
She is likely to go broody again (probably about the same time next year). Either break it quickly or if you decide to try hatching again, set her up separately from the others. Sometimes they do better the second time.