Ah, yes... even having Denna from when she was 7 weeks old, she pulled that one on me a few times, too. If we were leaving a park and she wanted to stay, she'd drop to the ground behind the car - in the parking lot - and not move. Sometimes a treat would work, but when those stopped, I just got in the car and started the engine... she JUMPED up to get in the car right quick, then, not wanting to be left behind.
It's a major mind game.... If being nice doesn't work, go the opposite... you need her to go outside, go outside and leave the door open, then start yipping excitedly like you see a squirrel, and see if she'll come join you.
Time for bed... turn out the lights and leave her where she is, alone, without you. Assuming it's ok for her to sleep there... once you get to the bedroom, clap your hands or make some other interesting noises to make her too curious to ignore coming to see you... and/or start a new habit where she gets a treat AFTER she's in the bedroom tucked in for the night - and it will need to be a really high value treat to start, so it's motivational.
Do you think there's any reason why she wants to lay down in strange places and has a hard time getting up? Could her legs/joints be stiff or sore? How active is she otherwise? Do you have her on any supplements for joint health? Is she overweight? I didn't think Denna was heavy, but we still found 10lbs to lose, and that's helped her perk up a bunch, too.
PS - welcome to the forum! Would love to see a picture of your pup. Click on "upload a file" to add a photo to a post.