It depends, but you should only have to file one state: Illinois. The reason is that Illinois and Wisconsin are reciprocal states: they agree that you only pay state tax where you live (IL) and not where you work (for her, WI). If only Illinois taxes were withheld, it will not be necessary to file a Wisconsin state return of any kind.
However, if Wisconsin tax withholdings were mistakenly withheld, you may file a Wisconsin return with a zero income using the Wisconsin Salary Allocation screen in the screenshot below. This way, all Wisconsin tax will be refunded. In addition, you may file Wisconsin Form W-220 (click on link) so that her Wisconsin employer withholds IL taxes only. Please see this FAQ for more information on reciprocal states https://ttlc.intuit.com/replies/4776822
Please note the following screenshot to zero out your Wisconsin income if necessary to do so:
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