The weapon you chose from the sitting room was the wrench. While kneeling beside the vanity, you hold the wrench so that it clamps between the back of the mirror and the front. When Alice walks in, you turn the wrench so the glass shatters but doesn’t fall. Alice hears the noise and sees her reflection, but it is refracted by the angled shards so, in her confusion, she throws the hatchet at the mirror. Now defenseless, you take the hatchet from the mirror and throw the wrench at her so she puts her arms up in defense, then use the hatchet to hack at her arms and keep hacking until she is dead. You are safe.