She says she is worried about having to pay 47k in capital gains in 3 years which is a big chunk that could go towards building the house.

Be a DON'T WANT-ER - always be willing and ready to walk if you can't get a good deal - And understand that you can always come back to that seller later and begin Second Stage NegotiationsAsk the 7 wordsAlways consider a subject to offerAlways ask for seller financingUse the Study Period Clause with right of possession to control properties without cashOffer seller participation - this is a great way to close dealsOffer something other cash - a note secured by your other equities, an unsecured note, a Principal only mortgage (using this technique you can offer more for the building since you are not paying interest - and as you know a direct reduction mortgage will pay off much faster.

I also pay a 1,000 finders fee for any unlisted property that someone tells me about that I buy.

Sadly, I don't know what the solution is, but I can guarantee that if more STRs get shut down there will need to be an increase in taxes coming from somewhere. 

But she wants to pay by credit card.

Someone would have a hard time convincing me that paying to tear it down and build something new would make sense.

As Dave ramsey recommends of not taking on a house mortgage thats more than 25% of your monthly take home pay.

Paying off my house and increasing my heloc to invest in other properties?

Go to your favorite search engine and look for "fake pay stub" and you'll see what I mean. 

Well in this new model you would essentially pay your investors 7% in the form of a debt service, therefore when you decide to do a cash out refinance you pay your lenders their 7% and you own all the equity in the property that you acquired.