1) 50% rule is a well accepted generic approximation 2) hundreds of underwriting has shown it to be fairly close for my underwriting for a SFR purchase in San Diego.  

I invest in Boise, ID and do quite a few BRRRRs, LTRs and STRs- varying degrees of success depending on how much equity we can force and the type of back end financing we can find, but the tax benefits are great and it's a rapidly growing market and Idaho is probably the most landlord friendly state in the nation. 

It's acceptable as an area though the flips I saw weren't great quality.  

So your results will be a degree lower than local investors. 

One thing to consider on the credit card option is that a lot of contractors don’t accept them so that could be an issue.

Of course, that is only if your intent is to hold it long term.If your goal is to unburden yourself from managing the property yourself, you do have options that offer degrees of hands free management. 

She's not going to have any leg to stand on in court if you get that far unless there's some explicit language prohibiting the owner from assigning responsibilities to another legally authorized party, and I'm guessing there isn't if another PM company was maintaining the lease and provisions - and the fact that the tenant was voluntarily working with the other PM confirms the acceptance of an authorized agent even if it's not explicitly stated, the same way if you accept rent from a tenant after a lease expires you imply acceptance of the lease terms continuing (which is why you should always have a holdover provision). 

Once the sellers accept the offers.. 

I don't think a degree will help, I'd sign up for courses and learn as much as you can.

If you are broke and trying to quit your job asap, the answer will be much different than what an acceptable answer would be for a professional investor who is a multimillionaire.