Ever since she was a puppy (she’s now 12) my dog has always gone out to poop immediately after eating. I think it’s just a natural instinct. However if it’s a sudden behaviour change it might be a rebellious protest act against being locked in the crate, particularly if she doesn’t do it when she’s out of the crate. Sudden pooping and peeing where they’re not supposed to, with no underlying medical cause, is usually the dog telling you what she thinks of the current situation. Perhaps you could leave the door unlocked for her but not for the younger, more aggressive dog?