New tenant relations

[Kyle Beckwith]

Our newest tenant has been in our single family home 1 month and we’ve already had some issues. 1. rent was late and they are upset with us for making them pay the late fee. 2. A sink was added in the basement for her hair salon (shark bite fittings on copper. Not acceptable/not up to code). Lease clearly states no alterations. 3. I’ve also been over there for a few more handyman items than I should be responsible for but I have taken care of them in good faith. 
There have also been a handful of repairs on our end (outlet not working, light bulbs needed replaced, hot water tank needs replaced). 
I feel like we’ve gotten off on the wrong foot already and want to make sure we have a good relationship moving forward. 
my question relates to the sink in the basement. I could let it go and it will probably be fine but if it does leak, I feel it will be my responsibility to fix it as it is now a fixture in the house. I’m also hesitant to make her remove it which she will obviously be unhappy with.

I have a plumber going this weekend to install new hot water tank. I can have him bring it up to code and charge her for it. 

I want her to know and understand us and the lease but also not let things get too far out of hand in the mean time. I want her to know that alterations are unacceptable but also establish a good relationship. What would you do? Any suggestions?