We know that adults can walk out of their lives at any time. Leaving their families and friends, if they choose. IMO, LE does not believe this to be the case. I do believe it's a criminal investigation but at this time, I don't suspect her husband or anyone else in her family of foul play. I do believe she left her home on her own accord the day she went missing.
I also think it's possible, as an example, she texted her husband or one of the girls her intention to head out for a bike ride. Perhaps it's unusual for her not to respond to texts or phone calls after a period of time and that was alarming to her family, who then asked the neighbor to check in on her.
Again, I believe LE suspects foul play, has some sort of evidence of it and they certainly don't want untrained volunteer searchers trampling over a crime scene. The family, with the exception of the nephew, who is probably not "in the know" is being tight lipped because that's the STRONG recommendation they got from LE. I don't however believe that her husband or children know any details of the investigation either.