Anything is possible.
Yes, like you, I often consider other angles. She could be in hiding and voluntarily missing for her own reasons. I followed a case like that once. (People were mad at the missing-on-purpose person after having been very worried and so much money spent on searches.)
She could have been abducted by a stranger and held captive. Or some serial killer could really be preying on people up in the area of Idyllwild. She could have gotten hurt or lost and hasn't been found. A hitman could have been hired to do her in. Someone on the 116 acre property could've harmed and disappeared her. Or someone wanted her out of the way and stood to gain. There's probably more I haven't thought of yet.
Yes, it's good to consider other angles. It's just hard to sleuth other angles without more information. I apologize if I've potentially focused us too much on the financial angle, but I was able to try to sleuth it by public information so I did.
I do think it's possible that she has gone missing on purpose if she feared for her life. I also think she could have gone for a hike, gotten hurt, and not been found. And I think there could be someone who might have wanted to hurt her for an as yet unknown reason.
I wish we knew more about who works on Dia's properties. So far I only know about Diana (Air BnB) and Dia's fiance. But there must be others. Dia is 66 and her fiance 71. It's a lot of work to take care of ranch properties. Behind the scenes I've heard there are some women who help with apple picking. But for those of you who own horses and other animals, isn't there a lot more work that needs to be done?
What about possible regular delivery of feed and other supplies to the properties? Would a delivery person(s) have regular access to Dia's properties?
What about plumbing, electrical, and other types of work that might have needed to be done on Dia's properties? Could a trades professional(s) have easy access to Dia's properties?
We don't know anything about Dia's property at 28893 Bonita Vista Rd. That property appears to be a mobile home on 5 acres. This is not currently listed on the Air BnB site. Has Dia been quietly renting that home (ie not listed on an internet rental site) to anyone? Could someone who works for her stay there (full-time, on occasion)?
Per early news reports the family (? who exactly) said Dia went missing at around 2:00 and was heading toward the Garner Valley area. Dia has a property on Tool Box Spring Rd in the Garner Valley area. How would the family know Dia was heading to that area? Were they referring to Dia's property, or to Garner Valley in general? Did the family maybe expect that Dia would be found at that location (speculation)?
Jash asked a great question about whether Dia's gun might be missing. Unfortunately we don't have an answer. Her fiance indicated that if she had gone for a hike she would have taken her gun. But IF it's missing then maybe Dia, or someone else, took it for another reason??