So Bella lives in a huge house (which she used to share with her husband). It's almost a mansion. However, she's a librarian and as far as I know librarians are not characterised by their brilliant salaries.
Now, you can assume that her family is filthy rich and she got the money from them or guess that her husband must have had a large income. That would be the starting point to any theory about his whereabouts. Are guys in the military paid that much in the USA? Policemen? Special-ops? I don't know, I'm not American.
Anyway, for me all those theories are wrong. Obviously, her husband was a top FedEx executive who was given up for dead after being in a plane crash in the Pacific Ocean while on duty. Bella refuses to accept his unexpected departure.
As for the locked room, it has nothing to do with her husband and all to do with Quinn. Let's just say that Bella's passion for plants is not restricted to orchids and succulents.