Yep. Broody chicken. Very normal. Her hormones are screaming HATCH EGGS! Broody chickens don't lay eggs. Being baby crazy does not require a rooster.
If you want her to hatch eggs you can put fertile ones underneath her and they'll hatch in about 20-22days. (Best to isolate the nest so other chickens can't get in if you can.) You may find some on craigslist or get some shipped. If you chose to hatch, make a plan for the chicks, ESPECIALLY extra roosters, even if it's just "give them away for free on craigslist".
If you DON'T want to hatch you'll want to "break" her brood. The best way to do this IMO is a dog crate on cinder blocks with a fine wire bottom, but any wire bottom cage works.
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Here's my broody australorp getting broken. She went in every morning after getting let out, and put in the coop on the roost bar with her sisters every night because it's not safe for our chickens to be out in the run at night. If (ONLY IF!!!!!) you have a secure run, leaving her in the crate in the run is better. She is not permitted to roam with the flock until she lays an egg or is otherwise no longer behaving broody, whichever comes first 'cause she'll sneak back to the nest. If she tries to sit in the nest box? Still broody! Back into the broody buster with her.
The goal is to get air flowing underneath her so when she tries to sit like she's nesting it feels cool and breezy.
If you don't break her brood she may sit for MONTHS trying to hatch eggs and starving herself for babies that will never come so it's best to pick one or the other.