did you use any type of strategy such as the calculator like the one from bigger pockets or did you guys have your own technique?

I used this exact technique on the home I'm currently in and about to convert to a rental in a couple of months.

So consider the option of adding a second ADU instead of enlarging an existing unit.

You must have checked out the IRS website. https://www.irs.gov/businesses/cost-segregation-audit-techniques-guide-chapter-3-cost-segregation-approaches

She's not comfortable with the more sophisticated techniques yet, so I just want to pay her back quickly. 

Well, you could be a hard money lender and get 15% more safely than doing a fix & flip.Or you could use this technique  https://www.biggerpockets.com/...Or maybe this https://www.biggerpockets.com/...

You can educate yourself through real estate investing books, listening to podcasts from notable investors who’s techniques match your interests, or read blogs posted under major finance blogs such as Forbes.Another way to educate yourself is to attend workshops that can offer hands-on knowledge.

They are permitted to publicly advertise in a cost-effective manner.Business are permitted to use social media and other advertising techniques reaching a much broader group of investors.Businesses have the freedom in making disclosures to investors which can enhance an investors interest in investing, likely to solidify more deals for the business owner.Financial statements produced by the business for investors do not need to be reviewed or audited by an independent accountant.

If you do have multiple options for property managers, definitely ask them about there policies, payment methods, tenant screening techniques, etc.Here's a great post I found too! 

It's far cheaper than a plan change or new envelope opening (adding or enlarging windows).