The assumption here is that the rollover was directly from the 401(k) to the Roth IRA. If she rolled directly from the 401(k) to a traditional IRA first, then converted the traditional IRA to Roth, she would receive a Form 1099-R from the traditional IRA for the distribution and conversion to Roth and it would be this Form 1099-R that would be reporting the taxable conversion.
