When dangerous robbers invade her remote country manor, a stubborn elderly widow must use her intimate knowledge of the building and her collection of ancient weaponry to fend them off.

Sounds like a cool movie Paul. What about the logline below?

When robbers break into the house of a recently widowed old woman, she must use her intimate knowledge of the house and her collection of ancient weaponry to take her grief out on the robbers.

35 words,

This reads like it could be a good comedy. Have you considered changing the genre?

"When thieves break into her sprawling excentric manor a reclusive millionaire must use the secret passages and her collection of antique weapons to fend them off."