For this fight you will have to get a handgun and ammo.
How to fight mia in the attic.
During the second encounter mia wields a chainsaw which can easily rip your apart if you are not.
Use fire aid and then move towards the attic and lower the stairs by hitting the red button.
Hit mia with the axe until she collapses again and the next step will be going to the attic of the guest house.
Upon arriving there collect the handgun from the table and walk around the attic.
Once you have collected everything you need to head to the attic in order to start the fight.
Luckily by the time you have to face her you have access to the m19 handgun.
Now head towards the attic for your final fight with your wife.