There are no explanations for the sandwich affair which seems to be pure malice on the part of the MIL, but when the LW claims they got along fine in the beginning, it's rather odd that she can offer no explanation for this sudden change except for an outburst of racism.
As I said, maybe I'm just cynical
I've seen it with my own brother.
He was dating
a woman (let's call her Meg) who was born in Asia (we're white) & came over here when she was young. Her parents were always nice to DB while they were dating
but when Meg got pregnant all heck broke loose. Granted, my family didn't have the best time of it either & we tried our best to be supportive but Meg's parents insisted my nephew be given up for adoption (DB & Meg didn't want to get married, they had actually broken up). As Meg was not allowed back into her parent's home until after she had given birth, she ended up spending a lot of time with my parents since she lived in my hometown to go to college & DB was going to another school out of state. My mom had to be the one to take her shopping for maternity clothes & go to doctor's visits!
Meg's parents never wanted to see the baby even though my nephew's adopted parents practically insisted we become part of their lives via an open adoption (which we are eternally grateful for). My family has lost touch with Meg but from what we've heard through the grapevine, when Meg started dating
another non-Asian & got pregnant again (but she did marry that guy), her parents disowned her. It was hard to go through all of it for us, I can't imagine how hard it was on Meg. Very sad.