Our landlord altered our lease after we signed it, and is trying to hold us to the new agreement. Does her altering the lease as it was originally signed void the agreement altogether?

Please provide more details. While it may not void, it can not be inforced. If there was an actual illegal fraud, it may put them in breach and allow you to get out of contract. But remember if they don't agree to letting your out, you wlll have to prove your case in court