Her crime? Failing to register as a foreign agent as all Russian media now has to in the states. Journalists.
If she had registered, she would still be doing what she was doing. A gun nut, she sought to weaken Russian laws. Everything she did was in the open. No laws broken except failing to register. Her "confession" came as a plea bargin after months of harsh incarseration.
After slandering her as a Bond "honey pot" spy, she is now locked away so Americans can be safe for another 9 months at not minor expense.
Why not just deport her?
Putin defends her actions here. He would, of course, have other feelings about her saying and acting as she does in Mother Russia.