Got the heat under control but still got a problem

[MamaL]

I have one chick who keeps opening her beak and extending her neck. I tried to look to see if she had something stuck in her throat but couldn't see anything. She is chirping fine and strong. I have no idea what could be wrong. She is running around fine, sleeping fine...but she's doing this opening her beak, stretching her neck thing......any thoughts, or advice?

 

[MamaL]

Some more info: bedding is aspen that covers newspaper ( could she be eating the newspaper?), water has ACV and GSE in it and regular chick feed is what she's been eating.

She is about three weeks old and is a buff Orpington