Thank you everyone for your feedback, and approach recommendation. I believe Tom V recognize what is going on really well.
Usually, I am really nice when I picked up a phone call from tenants concern. I use phrase like "thank you for calling", "I will address your issue and concern immediately as I know your concern is very important", "I am sorry for the inconvenience", "I am really sorry, I could not make it as I am with my family right now and let me stop by at 8:00 AM tomorrow" ..... etc.
Other 6 tenants that have the same negative impact understand the situation and trust that I will take care of this promptly, but why this only tenant. I told her straight up in person that I am feeling like you are bossing me around and that you are micro-management my ability to response to the hot water boiler matter. She told me that nothing is personal and it is just business. Remember, I just bought this building 1 week prior. I understand that I am responsible for addressing tenants concern, but I don't intent to have a boss whom is my tenant. One boss in my rat race is enough, and that is why I am trying the real estate job part time to build enough passive income to get out of the rat's track. If it causes more headache and dread to manage one tenant that required tremendous attention and response every minute, then maybe this tenant should be removed as she/he might not fit in the community or business model.
Story: The next day, I scrambled and called 6 plumbers and finally got someone to come down the same day at 1 PM to fix the issue. They overcharge me substantially, but it is worth the cost. The following day, she called me again, and she told me that she has a breathing issue, and would like to move my commercial trash can a bit further from her first floor unit.
Today, I am going to text her and let her know that "mam, I am showing your unit to build up tenant wait list just in case you have to leave in the near future. I believe as a tenant at will, I don't need to give her any reason to give my 30 days notice.
FYI: I never called the other plumber who told me "nothing was wrong with my boiler and water flood the basement from the boiler of interest".