If a person buries someone in a church cemetery plot that is not theirs, can they be forced to move the body?

This is a strange situation.  Assuming that "reserved" means that your Aunt has a legally enforceeable contract with the church to allow her or her designee to be buried in the specific plot, a Court can compel the offending party to move the body.  Depending on whether the Church sold the land to your Aunt, or just sold her the right to be buried there, the Church may have to be named in the lawsuit. The Church cannot "settle" the dispute unless all parties agree to be bound by itd decision.  Although it has a right to not have a body buried on its land without its permission, it cannot enforce that right without the Court's help.  If the offender refused the Church's direcitve to move the body, it would probably have to get a Court order to compel the offender to do so, although it may also be able to move the body itself, and then go to Court to compel the offender to reimburse it for any expenses incurred.