As a sister of battle player I can tell you that sisters are not under the Inquisition (Unless you mean the Inquisition can requisition them, in which case an Inquisitor can requisition anything he wants, the only people that really refuse is Space Marines and the Mechanicus). The Sisters of Battle (and their non combat commardes) are part of the Ecclesiarchy, the Imperial Church. But why do they have an Inquisition Symbol on their models? Actually that is not an Inquisition symbol but a Adeptus Ministorum symbol (The Ecclesiarchy).

Edit: Will this also be free, casual or advance?