Squatting???

"Squatting" is when a chicken crouches down, with its wings slightly spread. This often occurrs when a rooster walks up (so that he can breed her), or when a dominant member of the flock, or a person steps towards her. Chickens "squat" prior to beginning laying; the time between squatting and laying varies. My chickens usually start squatting about two weeks before laying commences, but it depends on the bird.

What your bird is doing now is probably preparing to lay. Chickens will often go into and out of a nest box a few days prior to laying, or on the day they lay.

You chicken is not a Copper Marans. She looks like an Easter Egger due to the color pattern and the pea comb.

 

That sounds like it could possibly be the start of broody behavior if she starts sleeping in the box.

It is not squatting. The squatting is actually a mating stance. It will happen when the birds are out in the yard and you walk up to them. They will stop moving and crouch down for a second like you are their rooster.

 

This is correct. ^ There's also the possibility that she's become broody.

 

My pullets started squatting (The stance they take when they are accepting a rooster) when I walked by at about 18 weeks and I was so excited because I knew they would start laying soon. My pullets would go into the coop and just sit in the nest box for a while and then leave and then a couple days later they started to lay.
I would say your chicken isn't a Maran as Marans do not have a pea comb.

 

Exactly. And my girls become extremely stiff while in that position as well.

I have 6 chickens, the first one to squat was a red sex link on Aug 5th, the second to squat was a black sex link on the 8th, and I got my first egg last night () Two more started squatting today, one barred rock and another black sex link. All my chickens are 17wks old

 

I wouldn't call her head gear a pea comb. A pea comb should look like exactly that, a pea sitting on their head. She looks like she's got a straight comb mixed with something else. There are lots of different comb types: straight (or single), rose, walnut, cushion, strawberry, buttercup, pea, v and carnation. And, crazy things happen when you mix any of those together
I had a Silkie/Orpington mixed rooster (so walnut x single comb) who had a comb alot like your girls, it sat up but was wavy.

 

She could be egg-bound.​

 

here's a link with pictures of combs
https://www.backyardchickens.com/a/the-8-comb-types