How close is she housed next to the existing birds?
If she's been right next to them, then let her out and see what happens - if she is carrying any type of disease the others have already been exposed.
Your view of "Aggressive" may be different than mine - for me, if it's pecking, chasing, posturing with minimal blood drawn (i.e. a small peck to the comb that bleeds) is o.k. It can take time for birds to settle down with one another.
Observe interactions and just see how it goes.
Thing is, some of that behavior in your description, I would probably deem "normal" some hens do rule nesting boxes, but I would have had to see it to even know. Hens can be very dramatic at times. If you are used to docile sweet fluffies that get along charmingly, and this gal is quite bold, you may end up changing your mind keeping her.
See how it goes. Video is can helpful, if not, entertaining
IF you have her quarantined for observation, then leave her quarantined.