Vent-I can't check your mail for you! (Long story)

I would stick with your current way of doing things. If she can't hold up her end of the bargain, then that's on her. Maybe send two copies of your response letters/ pictures. Send one via regular mail and one via certified mail. Just in case she really hasn't been getting notification, my post office fails to inform us sometimes as well too. It DOES happen. But don't stop sending via certified, because you need that proof in case bio mom ever wants to start something and claim you never send her a response or updates. I'm sure it wouldn't cost very much to just send one copy via regular mail and another copy via certified mail to cover your butt.