Passive-Aggressives hate being laughed at. They hate it, hate it, hate it.
When she takes a subtle dig at you, either laugh and cheerfully thank her for the compliment (and come up with a way in which it's a compliment) or else laugh and say, "How could you forget my job title? It's like the easiest thing in the world, and I've been doing it for a year. Should I write it down for you so it will be easier to remember?"
She might escalate, but laughing and taking a PA-insult as a compliment will drive her bonkers and will force her to be outright rude to you. This will mean your husband will have to recognize what's going on, and then he can develop a spine and defend you to them.
MIL: Your jeans are tight. You must be eating well lately!
DIL: you know, I have been! Thank God I live in a country where food is freely available and people don't have to worry about starvation. I saw a horrible documentary on PBS about parents who watch their children starve to death, and it made me cry. So, how about those Red Sox?
Thus, s he escalates:
MIL: But that's no excuse to eat like a pig!
DIL: Oh, were you trying to insult me? I'm terribly sorry for not getting it sooner. Sweetheart, it's time to leave.
And then go. Take the car alone if you have to and return later on to get your husband. Let him enjoy some quality time alone with his parents.