Is the wife obligated to pay the husband the full mahr if she requests annulment due to her aversion to living with him and his ill-treatment, especially given that the reconciliation committee recommended separation without compensation?

If your sister's case reaches a Sharia (definition) court, the court is the arbiter of it, and only the ruling of a Sharia judge can resolve the dispute. If the reconciliation committee was established by the judge and ruled for a divorce without compensation, then the judge must enforce this ruling.