She is a good person who unfairly is the most unpopular statewide elected official in Missouri. That is not even an exaggeration. Polling data backs it up as do internal discussions.
I have no idea who Democrats will nominate for this seat but they may end up not performing any worse than Galloway would have. Maybe even slightly better.
I assume she's so unpopular because of the (D) next to her name. And her disastrous gubernatorial bid last year may have hurt her reputation, making her seem as "no different" from other Democrats to many voters in Missouri.