That isn't entirely accurate. She was getting deluged with lawsuits against the office she held. To date all were dismissed or she was exonerated. That was costing the state money to defend the office of Governor. There was also the constant attacks on her and her family and it was taking its toll. I think we can agree a governor hasn't gotten this kind of national attention before and not on the scale or amount of time she has. Dems from all over the US, not dems but ultra liberals, were doing and saying anything whether it was true or not and fueling hatred. She had to stop it and resigning was necessary.
Now I am not saying in anyway that furthering her political career wasn't part of it but not the biggest part. I still don't think she would make a good president though. Maybe vice president.