Peck her back, chase her a few feet for a few more pecks.....that's what they do to a subordinate.
Use thumb and 2 finger tips, be calm but fast and firm...get her on the head or wherever you can hit her.
Don't be 'gentle', but don't break any bones or draw blood....lol....
it can be hard to understand how much pressure/force it takes to keep a bird under control unless you've handled them a lot.
She'll squawk and scream but that's just alarm not necessarily pain from injury.
If a couple of those interactions don't do the trick,
use one hand on her back to push her to the ground,
again fast and firm, hold her there until she submits.
Might take two hands, I often grab the tail close to the body to keep them from getting away,
again just firmly enough to keep them under control, it won't hurt them.
Use other hand to peck and yank the feathers on the back of her neck.
Once she submits for a few seconds let her go.
At 5 months your pullet (not a hen until one year old) is probably getting a surge of hormones,
this can make them more aggressive. Are you positive it's not a male?