Dear Bree,
Still would not bad mouth a former employer. Be aware the deep pay cut is well worth it in the long run, as you can live with your conscience, and, sooner or later, their malfeasance will catch up with them!
Karma is real.
As for giving a reason, I would make a list of secondary nonjudgemental reasons.
Was a bookkeeper, and I have been in your predicament.
Be proactive in doing thorough research into a company before even applying.
When asked why you left, throw the question back to the company you are interviewing with, stating, I left this company in order to work with a company like yours, and give your reason based on your solid research into the company you are interviewing for.
Hope this helps.
Yours truly,
Monica