In addition, there are 2 types of yields, "Gross Rental Yield" and "Net Rental Yield".

I would suggest researching 10-15 banks and credit unions in your area (just google "multifamily lending in X area" and see who pops up) and talk to them.

In addition to checking out @Jim Pfeifer’s Left Field Investors, I’d recommend you go to Ian Ippolito’s Real Estate Crowdfunding Review and his Private Investor Club.  

What I can suggest to you is for you to familiarized yourself with the contract thus when you are near the transaction completion with the attorney, you would not surprise or ask basic question.

Should I create a new lease for both of them, an additional lease for her, an addendum or anything else I missing?

I have a clause allowing 2 months rent free and $1000 a month rent for up to 4 additional months, thinking/hoping house prices will start to come down and buy then. 

Additionally, you can send that info to your preferred collection agency.  

The OP PROBABLY got a bad deal, and in addition had some bad luck.  

Curious are you still allowed to have additional financial requirements like no late payments in the last 6 months, no late rent payments in the last year or set a criteria like Debt to income ratio? 

My first suggestion is learn as much as you can about real estate financing and your local market first if you never done real estate investment before especially if your thinking of fix & flip. before venturing more than 1 hour drive from your home.