It was a standard checkup and shots so she wasn't aggressive then
This started happening after Friday when Zelda and Beck met the 2nd time and Zelda felt her position as family pet was threatened so I'm starting to think that was the issue because she was pretty mellow but a tad high strung the week prior to the second meeting
Unfortunately everyone who could foster this cat I know already has 1 to many cats
Edit: Let Beck down for a hour and she was super chill but my mom kept telling to stop petting her in case she bites me. My mom who is scared of Beck now, literally donned a huge winter coat, heavy duty gloves, and a broom to protect herself. Also my mom accidentally dropped a box of palmiers (french butter cookies) and Beck tried to gobble them up (had to pick up everything that didnt shatter into crumbs while Beck hissed at me). She seems more mellow so that's good so guessing the stress of Zelda being territorial pent up all this aggression she let out on us.
I'm thinking your mom fearing her is also an issue. Not that I blame her at all, but cats sense fear and it can make them either aggressive (due to perceived enmity, and because they see an opportunity to dominate and climb the social ladder) or fearful. It's unfortunately a self-reinforcing loop, and breaking it is crucial and one of the first things that you see in shows like Jackson Galaxy's. But without physical presence there it's going to be hard to help you with it. Getting physical like using a broom on her is also very counterproductive, so avoid it unless your physical safety is at risk.
Frankly the picture looks bleak unless you can relocate her somewhere else for a while. Again, try contacting people in your area that, like us, are dedicated to these things. Once you get ahold of one, they usually know each other so it's much easier to find someone who can help. In the meantime, try things like valerian root and Feliway to calm her down, and try to have your mom interact with and even look at her as little as possible (cats perceive staring as stalking and aggressive).
Another thing that you can do is try to estabilishing dominance. That she hisses when you were gathering the crumbs tells me she's still in that street dominance mindset, and you need to estabilish someone else as the alpha to force her to mellow down. Zelda is probably not going to be that someone, and definitely not your mom, so if you yourself don't fear her, it's probably going to need to be you. When she hisses, keep calm and either tell her "NO!", or even hiss back at her. If you do this, please note what her reaction is, report back, and we'll move on from there.
I think I would try to lock her in a room for the time being, ideally with you there. That way she can get used to humans without the interference of Zelda, and your mom can relax around the house. Keep her in your bedroom with food, water and a litter box, then at night she can get used to you while you sleep and aren't a threat. Is this feasible?