I hate the idea of filing for eviction (she is single a mom with two kids), but I also do not want to be accused of stalking her while I try to catch her to speak in person and get a feel for what is happening.

Unless your state/municipality requires you to explain further, if they accuse you of discrimination or inquire as to why they were declined, simply state that the information they submitted in the application did not meet the stringent requirements for this unit.

We don't accuse anyone of drug dealing, we describe behaviors that we see, give them a move out date, offer to let them out of their lease without penatiles and fees, and to return the deposit if the leave the place reasonably clean.

Keep in mind there is a difference when you are discriminating against people because of choices they made, versus things out of their control (race, sex, etc.)That being said, some people get overcharged, falsely accused and some simply make mistakes. 

My upstairs tenants recently wrote me an email telling me that she is suspicious of my downstairs tenant of dealing marijuana. She said her husband and her as well as our neighbor have seen strangers coming in and out...

But the last thing you want to do is have this third tenant accuse you, as the landlord, of taking part in some sort of illegal tenant lockout. 

After these expenses and all others split 50/50.I know this seems a little OCD, ( it would not be the first time I was accused of that) but it seems the most fair way to split, and possibly could prevent disputes or sore feelings.   

They made the accusation that we knew mold problems, but fraudulently did not disclose and therefore the lease is invalid.  

Castrovinci, when making his demand for $5,000, also told the landlords he had somewhere else he could go to live, the suit said.The lawsuit accuses Castrovinci of extortion, trespass, breach of contract, intentional and negligent infliction of emotional distress and interference with prospective economic advantage.Castrovinci has not filed an answer to the lawsuit.

I'm not sure what you're "very concerned" about and it almost seems like you are accusing me of shady dealings.