Assuming we are talking single family, very limited exit strategies/investor pool (high-end rehab/flip, STR/airbnb, rent by room model). 

Yes, diversify as much as possible within the limitations of the 1031e.With that much liquidity, she needs to be talking to brokers and large-scale property managers.

I use Cozy for applications, background checks, and rent collection.

#1 -  the concept of a HELOC (borrowing against equity whenever you want, up to limits) is fine and I agree that from what is posted this solution may be a good fit, but #2 - if you go to a bank and try to get a HELOC, I am 95% sure you rental properties won't qualify.

In California, you can pull permits as owner-builder - although I think you're limited to how many you can do per year. 

You could set it high, but then that would limit the renters that will apply.

Most banks will limit the income credit from the rental given your limited ownership (less than 2 years).  

Think students, new graduates or people with limited income. 

Would it be my safest bet to just say i'm interested in joint ventures and limited partnerships?

We've had a ton of interest but only actually received 2 applications (we listed it last week).