Difficult tenant

[Nat C.]

I have a tenant who is very frustrating. They applied for a house and wanted to move in immediately. There were tenants already there who weren't moving for another week. The applicants were apparently staying in a hotel. She asked me to get the old tenants out sooner as they couldn't live in a hotel (they are a husband, wife and a baby). I said no. She asked if I had any other properties they could stay in for a week. I said I had a room in my house if they wanted. I usually rent the room on Airbnb for $70/night. I gave it to them for $40 a night. They stayed at my house for 5 nights. They therefor owe $200. They paid the pro-rated for July's rent and the deposit to move into the house and said they'd pay the $200 later. Upon move in, she had a 3 page list of requests. These included new: New vacuum cleaner bags for a vacuum which was already in the house. A wooden strip added to the front door as she thought the gap was too wide. New electrical outlets for the whole house as the existing ones were old. There were some valid requests which I fixed straight away (AC wasn't cooling below 80, one electric outlet wasn't working, washing machine wasn't hooked up properly). When August rent was due, she paid on the 11th and gave me a doctors certificate and said to please forget the late fee. The lease calls for a $75 late fee after the 5th plus $10 per day for every day it's late. It says in the lease that illness will not excuse the late fee. The tenant is owing $200 for the stay at my house plus $125 in late fees. She is seemingly refusing to pay and not responding to my texts or phone calls. I am on a very friendly basis with the tenant and don't want to become unfriendly but she needs to pay. How should I proceed?