Chief of Staff Ed Oatman said Stender had to file because money is coming into the campaign but that she is not ready to jump into the race. However, Stender has indicated she is strongly considering another run at Ferguson.
Democrats have zeroed in on the seat after not giving it as much emphasis as many others last year.
Ferguson has been preparing for another bruising race, having raised $418,000 in the first quarter of this cycle. Stender has not been raising money but has instead been preparing for a state Assembly reelection bid this year.
Other top Democratic candidates have yet to emerge to challenge Stender in the primary.
Stender and Ferguson did not return calls seeking comment.