Need help understanding cats behavior.

we brought in a stray cat about 3 weeks ago, she seemed friendly enough with the occasional hissing and scratching which i chalked up to her adjusting. she doesn't mind being pet however her tail, stomach and legs are off limits, her back is fine for a pet or 2 sometimes and then she will swipe almost without warning and hiss after. after the 1st week we got her into the vet for vaccines and general checkup, she seems like a perfectly healthy 8ish month old cat. we also have her confined to a roughly 300 square foot room which is where we (me and fiance) primarily reside as we live with my fiances parents. She cannot leave this room because there are unfriendly dogs downstairs so we're making the best of what we can. she has quite a few things to do and we are ordering her about $250 more worth of stuff in 2 days. she will have 2 litter boxes, a variety of food, plenty of treats, a second cat tree that's about 80 inches tall and she already has a cat tree that lets her see out the window.

2 weeks go by and it seems like when she gets too playful which is quite often, you cant reach anywhere near her or she will lunge for your hand with claws and begin hissing again. Recently she had me cornered and she had a look in her eyes i decided it was best to wait to step around her and it was the first time she jumped off the floor after my hand. i also spend a lot of time on the computer and when she lays on my mouse pad and i try to move her she claws and then hisses. it is worth noting the only time she has growled was one time when i tried moving her against her wishes and at the vet. she will be spayed in 1 week and im trying to understand this behavior and whether or not it will go away after the spay or what it is and how it can be worked on. honestly the biggest issue primarily is when she lays on my mouse pad and wont let me move her, which seems minor but considering that's where i spend my free time its fairly detrimental.