The dog is being annoying- advice?

Ok so over a year ago I found a mouse in my house. Mia chased it from behind a shelf and across the room to under a storage container. I set out traps and the mouse was never seen again. About a week later the lady sharing the wall with my duplex said she found a dead one in her house. This is the only mouse I've ever seen in my house. I hate mice, btw.

Anyways, that set Mia off. She went crazy for it and for the entire year + several months she runs back that shelf and barks at where she saw the mouse. I think this has mainly just been self-rewarding. She gets excited- sprints to the back room and barks at the mouse. It's probably not a good thing but I can tell her to knock it off and she stops and is fine.

This past week... her behavior has changed. I was in the shower and I start hearing her barking in the back bedroom. It is a different kind of bark. Usually she will just excited bark/screech at the spot but this is a very relentless, uniform kind of bark. It's the kind of bark she usually makes at something- like if she trees a squirrel. By the time I get out of the shower (hurrying), she's been barking constantly and is now scratching at the shelf. I remove her and shut the door. Well, the door only pulls closed, it doesn't shut and latch so she can open it herself. We repeated this several times then I eventually put her on the couch and told her to stay there.

It's been about a week and she is trying to get back there to bark almost 24/7. If we're doing something together, she will ignore it and stick with me. If I put her on the couch or somewhere, she'll stay. But she just keeps going back and barking and scratching at almost every opportunity. Her behavior has changed too. I keep catching her doing her 'nosework sniff'. Deep sniffing, nose to the ground, shoving her nose behind things and under things and sniffing loudly. There's got to be SOMETHING, right?

I am thinking... there must be a mouse living there. I can't move the shelf by myself. I haven't seen any indication of a mouse. And trust me I've been looking. but she is so relentless about it...

We have moved the shelf in the past (it has a hollow base) thinking that a mouse might have started living in the base and there was nothing.

Anyone have any advice?

get a blacklight and look for mouse pee trails around the area. if they venture out even at night when you dont see them, they WILL pee errywhere

Zach's parents dog used to do this, all. the. time.

The ONLY thing we could do was constantly redirect her. It IS a self-rewarding behavior, and it often becomes an OCD type obsession.

I don't know if she's crated when you go out, but I'd definitely, if possible, keep her out of that area. Either a child latch on the door, put a chair in front of it, baby gate, or shut her in another room. Only let her in that area when she's directly supervised, and keep redirecting her attention. Make sure she has something else to do, like a RMB or Kong or something.

Traps for the mice, duct tape for Mia

We end up with a mouse in our basement every couple months. Not sure how they get in, but we just leave a trap or two up and rebait periodically. Since one of Brie's litterboxes is down there we put the traps inside a length of 3" irrigation pipe, long enough that she can't bat at it, etc. Might be worth a try. Otherwise it looks like you may need to move that shelf again :/