After burning the Braithwaite Manor in the end of the mission Blood Feuds, Ancient and Modern, you can return to the location some time later to find the burned down remains of the house. There are still armed guards roaming the property who will shoot you on sight (killing them will result to honor loss) so try to sneak in.
For some reason, Catherine's burned corpse is left rotting in the open. You can loot her brooch from her body. You can keep this unique item or sell it for $25. There's a lockbox in the other side of the wall near her containing a gold bar.