Hmmm. Am I there yet?

It could be the teenage stage. Or it could be her personality is still developing or something else. As far as how long it lasts... well, I'm still waiting for Jaia to outgrow it and he'll be 3 next month.

What I have done that helps a lot is to make those borders REALLY clear, be super consistent and offer consequences for stepping over the line. Those consequences would depend on the specific behavior, of course, but they don't have to be painful or scary. In fact, with the new stuff I'm learning about how some competition obedience people train their dogs, I can see me making a "game" out of obedience a lot in our future.

Never give her a chance to "skirt" a command. Don't give the command unless you're in a position to enforce it. Only after it's proofed (she does it 100% of the time) should you give the command when you can't enforce it (off leash or far away). So, the consequence for skirting a command is that mom "makes" her obey, so she might as well do it anyway.

Just enforcement of the command should be enough. Assuming that she KNOWS the command, if she doesn't lie down, don't repeat the command, don't walk away. Go to her and calmly and gently physically manipulate her until she's lying down. Then praise. Most importantly, think before you give the command... "Can I enforce this if she blows me off"?

This is what I have done and it's working well.