Both are on autopay, have insurance, keep their places clean, and are civil to each other.The upstairs tenant is a school teacher in her late 40's. 

I'm no exactly new to BP but have never introduced myself or gotten involved. 

There is a ton of trust involved on both sides, but especially when you're the one shelling out the money. 

Do you assume the renters cover the cleaning fee?

If your goal is to grow your LLC, consider arranging all of your properties under an agreement with your LLC to manage them & take all of the legal steps to ensure that the structure is correct. this may involve creating LLCs in the state(s) your LTRs are in to own the property and your PM LLC managing those properties, so that you don't have a concentration of all of your portfolio in one entity.

What is likely to happen is you try to solve HER problem - just to have it repeat.You really cannot evict one person w/o evicting ALL OCCUPANTS.Know you think you are doing the right thing, but you are NOT.The only way you can/should assist the mother is if she files a police report on the other occupant.If mother is not willing to do this, do NOT get involved!

I cannot find anything specific to dryer vent cleaning anywhere.

I grew my rental portfolio starting with a house hack to rentals that are all clean BRRRRs.

And don’t pay anyone or sign anything before you get your carrier involved.

If you can get in with a real estate brokerage that is more involved with investors you will learn a lot more.