What exactly is a ridesharing carryover? Is this IRS, or a state issue?
Did the wife file her own MFS return in 2016? As @Just-Lisa-Now- points out, it's probably not worth contesting such a small amount with IRS. That's especially the case, if she can't explain why she didn't file her own return that year. But if other issues come up that require a trip back to divorce court, you can add this one to the docket.