I do have great credit and good income to cover the mortgage if anything goes wrong.

It’s far from a perfect rule but I do think it’s a little more accurate than people want to give it credit for.

You find the deal and let your partner bring the credit/equity. 

Refinance your rentals and reuse the cash.Add a Business HELOC "Line of Credit" on the extra equity. 

I have already run a credit check and everything is essentially perfect. 

I've been researching using Lines of Credit to pay down a mortgage (this one is for my primary home).

If you try to get a HELOC from a mortgage broker the rate will be crap (if they can do it at all), if you try to get a purchase investment property loan from a credit union or big bank then it'll take 4 months just to be declined at the last minute because your CPA didn't dot an i on page 7 of your tax returns, etc etc, you get the idea.

Will she allow you to run her credit?

The is a fee to use a credit card.

I did it... basicallyI took out a line of credit against my home.