My vote is option one.  

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A Solo 401(k) may be advantageous for self-employed individuals, offering the potential for participant loans, higher contributions, and no custodian fees, as well as higher contribution limits and the option for tax-deferred or Roth contributions.This post does not create a CPA-Client relationship.

I have considered turnkey properties as an option

There's too many investors who are front page news in Northern states re CFDs gone bad and Texas where lease options went bad and the state enacted buyer protections...Take care to all.   

It’ll save you headaches later if she tries to escalate things.Document Everything: Take pictures, write down the history of your interactions etcOffer a Transition Plan: Just like my client, I’d recomend offering her a temporary storage option nearby, or even a small rent discount, to show you’re not trying to kick her out - just keeping the property safe and up to code.

The other option, how I found BRRRR and learned some basics of it, was the Bigger Pockets book.

Otherwise, I recommend option two, using a personal loan.

Your best and most efficient option would be a DSCR cashout refinance, more than likely.

With countless loan options, complex terms, and strict lending criteria, it’s easy to feel overwhelmed.