From Stateline.org:
By contrast, the Republicans have serious concerns only about Arizona, the three open seats in solidly Democratic territory (California, Hawaii and Rhode Island) plus Nevada, where first-term Gov. Jim Gibbons has gotten himself into a series of self-inflicted scrapes, and South Dakota, where a strong Democratic candidate, U.S. Rep. Stephanie Herseth Sandlin, is planning an open-seat bid.
Hardly definitive, but this phrasing makes it sound pretty certain she’s going to run.