Her decision comes on the heels of former Montana Gov. Brian Schweitzer's (D) surprise decision not to run for the seat. The popular former governor's move likely dealt a blow to Democrats' chances of holding onto the seat in the Republican-leaning state.
Other Democrats mulling a run include EMILY's List President Stephanie Schriock (D) and Montana state Superintendent Denise Juneau (D).
On the GOP side, Rep. Steve Daines (R-Mont.) has been seriously weighing a possible bid.