Have you tried the web site Cat in the Bag (I forget the url. It has great ideas for escapees esp depending on the varying personalities of indoor and outdoor cats. An indoor cat like Bella needs special attention so I would think a humane trap near where she was last seen is NUMBER ONE but you indicated you had done all the suggestions and that was one believe. That leaves the option of hoping no one picked her up - - esp if they knew she is a Bengal and saw she was pregnant. I would call every vet in the region and even outside of the area and see if a cat like her has been brought in. Dos she have a microchip - esp bing so valuable.
Indoor kitties rarely stray far from their territory - they do not like to be away from their place. So if no one picked her up, she has to be close!
Good luck - I would continue what you are doing, g out , do a grid even - there is a pet detective that recommends that. Have you red Kat Albright's book (Think that is the name.) She has some great ideas as well.
I hope she is home soon!!!