My partner and I adopted a 7 month old cat yesterday, she seemed fine, we were in her safe room for a few hours at a time, and she was curious and played and explored just fine. No hissing, and only a low growl when I attempted to let her sniff my hand, which is fine.
Today we were in her safe room, my partner had gotten up early and was with the new cat for a few hours before I entered. She was playing, and even touched and sat beside my partner. My partner then left the room, leaving me and the cat, she jumped up near me, I said hello, she hissed. Then she went to the door and began meowing/yowling at it. I left her in the room, and after telling my partner she went back into the room with the cat, who then also hissed at her and hit my partner's leg with her paws. So we left her in the safe room, but we can still hear her yowling from behind the closed door.
I also want to mention that she has not yet been spayed.
What should we do? I'm a little lost and any help would be appreciated, I've owned dogs before but never a cat.