It says she resigned from the Attorney General's Office, not just the Rhoden case. JMO, she may be planning to run for public office. If so, she can't be in the middle of any one of these trials, which will probably still be ongoing in 2022. JMO.
She's done fantastic work so far on the Rhoden investigation, prosecution and pre-trial activities. She's in a very good position to run for higher office, maybe even the next AG.
She's had a pretty good team at the AG's office helping with this case. There are probably more than a couple of prosecutors who will be more than able to take over when the trials get started. If they're going to make a switch, this is probably the most opportune time, as the trials are expected to begin later in the fall or winter.
ETA: Here's the guy taking over:
Anthony has been involved in the case for a long time, too. He'll do fine as a special prosecutor. I think they're all ready to get these trials started. Its a long time commitment and a lot of work ahead, but they're ready.
ETA: I'm just speculating on AC's reasons for leaving the Ohio AG's office. She's a highly qualified and experienced prosecutor, there are any number of plans and options she may be pursuing in her future. Staying with the Rhoden Murders case is still a long commitment. If she had other things she wants to do in the next year or so, now is the time to leave. Yikes, she already been working hard on this case for the last 4 years.