In the "real" world, yes, wives would be and could be working to help support their families, but in the Godhard world, the husband is supposed to be the only one working while the wife stays home, ready to be joyfully available at any time, and raising the kids (until they can hand them off to an older sibling).
I think since Izzy's birth, Jill has been suffering from depression. She married the first guy that paid any attention to her and got pregnant within a week or so after her wedding. She probably thought everything was falling into place. Then Izzy was late, she had a botched home birth plan, and had to have a C-section.
After that, her husband had surgery on this mouth that did not end up the way they believed it would. She went to Danger America with Derick. My thought is she didn't mind the idea of being a missionary's wife as long as after a week she could go back home and it didn't happen this time. We have no idea what really happened to her during that time. If it was an actual serious issue, attack, or just the shower holder (or whatever it was) falling off the wall.
No one really knows what happened during Sam's birth. Derick goes off the rails on Twitter and quits the show (or a more reasonable thought is that TLC let him go). He goes to the church ministry school or whatever, he doesn't find a job, and now he's in law school Derick is too busy being a student, a pretend missionary, or whatever and not supporting his family. Derick does not want to work and he will do whatever it takes not to support his family.
JIll's life is nothing like what Gothard and JB and Michelle brought her up to think it would be like. In her world the husband is supposed to support the family and it's not happening in her life. She is not going to be having 19 kids like her mom did. Like many of us, life is not what she was brought up thinking it would be. However, she doesn't know how to adjust her thoughts and figure out "plan B."