I was planning on giving her the approval and moving forward to rent to her but my mother planted this seed in my head saying something seems off.

They may actually be investors or just plants for the co., which unfortunately is a red flag that pops up because it has been done so many times here on BP.  

Then you could live another 20 - 30 years off that cash-flow.The best time to plant a tree was 20 years ago.

How realistic would it be to plant walnut trees or lease it to cattlemen?

The Samsung plant was the largest investment to date at $17 billion.  

Your best bet is to start doing networking / planting seeds now.

Intel is a great example, who is building the largest chip manufacturing plant in the US right here, and it will be a $20 billion dollar investment that brings a few new thousand jobs. https://www.dispatch.com/story... 

We own several fairly large apartment buildings in the Los Angeles County area and our water costs us an average of $60 per month per tenant.I am fairly sure the cost for water tripled in the past 10 or 15 years and we would probably be paying more than $120 per month if we had not installed water-saving toilets, water-saving shower heads, water=saving bathroom sink and kitchen faucets and we removed all the laws, shrubs and trees from every property we own and installed rocks and only 4 to 8 cactus plants on every property.

However, in a captured market serving a refinery, you have to be aware of the risk if the plant shuts down for an extended time or permanently like some have done recently. 

Quick update, front yard rock is in, plants next.