She saved the letter as her ace in the hole, since Kavanaugh was doing well, she took a gamble and lost. She used Ford to raise money for the mid-terms, hoping it will help them to get the Senate back, and her sacred power. It is likely now, the Republicans will hold on to the Senate.
Feinstein is also slipping in her own polls. CA Reps can take her out by voting for her Dem opponent.