The fight with Lisa Trevor will be your last objective in the Mansion before you enter the Secret Umbrella Laboratory.
Make your way to the Main Hall in the Mansion and run behind the Staircase. Use both Metal & Stone Objects to unlock the Gate.
Use the Typewriter and descend down to the Altar for a final Showdown with Lisa Trevor.
A quick and easy way to defeat Lisa is to push the four Stone Pillars off the ledge. It will save you ammo and aggravation.
Hope it helps
All Credit for the YouTube Video goes to Kheapathic.