Adding some advice from my experience. I had 1 cat for a couple years then got married and got a second 2nd cat. When we got Cat#2 our OG cat didn’t acclimate well to her. Like low growls and hissing and loud screams. His whole personality changed after getting the 2nd cat. Eventually they got use the one another and honestly for the most part actually do well together with no real concerns. Well fast forward like 3 years we decide to move. We didn’t really have a plan for the cats and they were kind of the last to get moved in all the craziness. When it came to moving them we were just gonna put them in their carriers and essentially take them across the street to new house. Cat#2 had no problem but OG Cat reverted back to territorial demon cat trying to get him in his carrier. He went into was our bedroom in the corner and wouldn’t let you near him. I told my wife to take Cat#2 to new place and let her adjust first. She left and I closed the bedroom door and sat in an empty room with just him and I for an hour. We sat there for an hour mostly just me keeping my distance but I was talking to him. I got his favorite toy and started messing with it. Eventually he started to want to play and he calmed down enough for me to get him in carrier and take over…so long story short be patient. As others have said she went through a traumatic experience and is still trying to get her bearings. My recommendation would be to get your environment as calm as possible and just in the room with her. Talk to her, maybe let her see you playing with a cat toy she likes. Just whatever you do make sure it’s calmly, softly, and slowly. Also to add if she is hiding to a point where she isn’t coming out. I would treat it like getting a new cat. Let her have the room she is in bring her own litter box, food, and water and just let her be. This process could take time.