Many shops don't necessarily require a ton of experience but a strong work ethic and ability to learn.

So, the things that stand behind it such as a deposit, proof of funds, etc make the seller know that the promise isn't idle and has a strong likelihood of closing. 

Then, assuming you have a contractual arrangement with your buyer, just represent him/her as fiduciary and the seller as Customer, in a normal brokerage transaction.The other option is to just put the property under contract, then assign the contract, but again, this needs to be fully discussed in advance with her broker, then fully disclosed to the seller, so they can't come back later and sue you for making "too much" on your transaction fee.I strongly suspect that your sister will be required by her broker to use standard contracts and forms made available by your state's real estate commission. 

Very strong and the 1% rule works very well here. 

I was wondering if anyone had any strong recommendation or contacts.

As @Joe Splitrock and others have mentioned, the simple answer is to go back to work in the same field you were working in, hopefully quickly and in a higher paid position, and continue building a strong employment history in your area of expertise. 

There is strong housing demand in all of the 9 county area but "30 minutes from Knoxville" includes both areas of exceptionally high and limited, price sensitive demand.  

I’ve got strong equity positions with a few different rentals and would like to have access to additional cash, but every lender I’ve spoken with so far can only do HELOC’s for primary residences.

And re: changes in the market, what if the market is continuing to appreciate strongly?

I strongly suggest you get a new PM.