MIL needs to be more assertive re: the mamo and u/s results. Remember we weren't all so willing to speak up early on in this journey.
That said, maybe she'd like to come here and read our posts, etc. It just may make her think about things a little differently. Or is it possible that she's an "ostrich" type and doesn't want to know the true story.
Just some of my thoughts on this kind of situation. I always think the sqeaky wheel gets the most attention. Drs. today are perfectly willing to let things go if the patient doesn't push the issue. Ins. companies make everything so much more difficult, so if the patient isn't requesting further tests, they're not going to suggest it.
Of course, if 6 mos. down the road there is a BC dx, MIL will have lots of time to think about how quietly she accepted their original "come back in 6 mos."
In the depth of winter, I finally learned that within me lay an invincible summer. Albert Camus