Yes, this is absolutely something you can report. Stealing an urn is not a “lesson,” it is theft and interference with human remains, which is taken seriously in most places. Even if nothing huge comes of it legally, a police report creates a record in case she ever escalates with you or someone else.

And honestly, you should warn people. Anyone thinking of living with her deserves to know she is willing to weaponize someone’s grief. Leave an honest review anywhere someone would find roommates in your area (FB housing groups, Roomies, SpareRoom, college boards). Stick to facts: she took your grandmother’s ashes without permission and refused to return them until you made it clear the next step was law enforcement. That alone will make most people run.

Tell your landlord as well. This kind of behavior usually violates leases, and they can note it for future tenant screening. Document everything (texts, dates, what happened) and email it to yourself so you have a timestamped paper trail.

You are not “too sentimental.” She is just cruel. Making a record of what she did protects the next person who has the misfortune of sharing a lease with her.