I have absolutely no reason to think this, but in addition to having developed some kind of health issue that impacts her diet, I think Becky is unable or unwilling to keep doing midnight Wommart runs for snacks. Maybe the car finally gave up the ghost, or maybe Becky had a heart attack and crashed it. AL's upset seems bigger than just "my girlfriend is threatening to take away my access to McDonald's" and closer to "I have lidurally no way to obtain McDonald's". If the boys are moving out, Destiny is refusing to pick up the slack and agree to run to AL's side every time she calls ("I gave you money! I'll give you more money! Forget working a real job, just agree to bring me midnight McNuggets! WHY CAN'T YOU JUST BE THERE FOR MEEEEEE?") AND Becky STILL refuses to move away from her AL-hating family to a place with UberEats, then that might do it.
Or Becky was told she had to lose weight for her health and took it seriously. Nothing bad happened, is happening, or will happen, and AL is just desperate to spin nothing into something to get her sympathy to make up for Norma hogging it all recently.
Coin flip, imo.