She was turned away from every other landlord or mega apartment complex because of her credit score (she went through a divorce) but I want to help her increase it because she has been great as a renter.

I am looking to renew the leases and increase the rents to market value.

I'm reluctant to do a refi since I have great rates locked in and I'm not 100% sure when I will need access to the credit lines from the HELOC, plus I'd rather avoid increasing my payments until I need the money.

The only way this might be attractive is if you have the property (park/pads)...That said, it's a low-class market...how many people in your city are really looking for mobile homes?...

My best guess is it would take around $60k to make it attractive enough to fetch $400k. 

Other investment (non real estate) opportunities look more attractive as time goes on. 

I found a 2 bed/2 bath with a fully finished basement which i turned into a 4 bed/2 bath, increasing the rent significantly. 

That has come up in a few recent podcasts about the need to create good deals as they are increasingly hard to find.I tend to focus in the same areas as you and have had the same dilemma, lower the rate of return you are willing to accept, or wait it out. 

Variable rates do worry me, especially with more planned increases this year. 

Since the property taxes increase substantially, and real estate being so expensive it is really to start real estate investment locally.