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She doesn't have Hobson's Choice. In Hobson's Choice, ONLY ONE option is there ... so, either take it or leave it.
Here Sonia is confronted with two choices i.e. MMS or Rahul.
This is a Catch-22 situation.
If she lets Rahul take over she is crazy; but if she lets MMS continue, again she is crazy.
If she is sane enough to let MMS continue then she should be considered sane enough to let Rahul take over.