Sidney Powell did the plea deal because she wasn't going to go to prison for DJT's sake - DJT's lawyers had hoped to pin the whole mess on his advisors:
She was the ultimate MAGA conspiracy theorist. Then she got charged with being part of a criminal conspiracy, and her tune started to change
www.rollingstone.com
Before her plea agreement, some of Trump’s legal and political counselors had been working to cast Powell as a “fall guy” in the election-related cases against him and hoped to shovel the criminal exposure and blame for the failed attempt to overturn the election on to her and others, in the hopes of shielding former President Trump. After all, this was the woman who pushed the idea that George Soros — or was it the CIA? or perhaps Venezuelan strongman Hugo Chavez? — was somehow involved in the rigging of the election against Trump. And she was one of the trio of advisers who pushed the then-president to consider imposing martial law rather than quit the White House.