My two cats (female liter mates) may carry on a bit if they see my wife or I
pet another cat, but the extent of their hissing or growling turns to the
cold shoulder to both of us for a half hour or so after we come back into
their domain.  Once we took care of our daughter's cat while she was on a
business trip and things were pretty tight, especially at first.  Within a
couple of days all three would lay down on the same bed, but there was
obviously an agreement that they would only participate in this group rest
period as long as no one so much as even moved any part of their body.
Breaking this agreement ment that each cat had to curse at the other two for
fifteen or twenty seconds, after which it was okay to pretend to rest again.

The behavior of the cat you describe seems excessive.  Perhaps she was
injured by fighting with her brother.  Check her out and if you find no
obvious reason for her behavior take her to a vet to see what might be the
problem.  If she is acting fowl for more that a couple of hours I suggest
she might need medical attention.

A bit. Female cats can be very attached to their people. My two are
indoor/outdoor and they are on friendly terms with 4-5 other cats on
the block that swing by regularly. One orange, fluffy guy who lives a
few houses away is their buddy, but when I gave him a pet, my Callie
chased him right out of the yard. That is simply not permitted :>

But that was the end of it. Her unhappiness didn't persevere for days.
Probably it's some displaced aggression towards the outside cat that
she can't express because she's indoors and can't get to the other
cat.

She is experiencing an episode of misdirected aggression.  One of my
cats has done this, but instead of taking it out on our other cat, she
takes it out on me, and it is very very scary.  It can take a while
for them to really calm down from these episodes, and you can not
hurry it at all.  I have even read it can take a few months to
completely recover composure from a very bad one - which yours does
not seem to have experience since you can go in the room she is in.
But just be extra cautious for a while.  And try to not let her see
any stray cats again if at all possible.  I have read that when the
aggression is taken out on another resident cat it may be necessary to
go thru a whole re-introduction type thing again, but hopefully you
won't have to do all that.  Just be careful around her for now.

Teri