To me, it's obvious that Meri has some deep, unresolved emotional scars related to her secondary infertility. I know because I went through some similar struggles when my husband and I were building our family. It's very difficult and can really take a toll on you emotionally. Only difference is I didn't have to grin and bear it as my husband knocked up other women a dozen plus times. How awful that your ability to procreate is valued above all else in the polygamy culture. And now, even the "new" wife has more children with Kody than Meri does, further cheapening her "worth" in the family.
I think Meri saw the catfish thing as finally her out from years of being unhappy and depressed. She was so ready to move on. When it all blew up, she was left not only hurt and embarrassed, but also mourning the fact that she's basically stuck with these people for the foreseeable future. Any hope for a better life seems over now. And the misery of it is written all over her face.