Hi Tee14,
I'm wondering if Siren would benefit from some regimented play therapy. It could be that she just has a lot of mental and physical energy to burn and nowhere constructive to apply it. Cats in the wild would normally spend a huge part of their day hunting, so when confined to a life indoors, all that energy can build up to "toxic" levels
. If you set aside a good 20 mins once or twice a day (morning and evening is ideal because cats are crepuscular - ie they're most active at dawn/dusk) to engage her with a fishing rod or wand style toy, or play a game of fetch with her, or hide catnip mice in various places for her to hunt for, etc, that might help tire her out a bit. Then when the session is over, feed her a meal of tasty wet food and she'll likely decide to have a nice nap after that.
Speaking of food, what does she eat? Diet can play a role in how cats feel and if they're eating lots of carbs in the form of kibble, they're more likely to be a touch irritable. Wet food is better for cats than dry, as you can read about here:
www.catinfo.org
Does she have any tall cat condos or other vertical space (bookshelves, window seats) that she can hang out on? Cats tend to feel more confident and relaxed if they can watch all the household happenings from up above.
Where are the scratching posts located? If they're tucked away in a corner, now would be a good time to put them more front and center. Place them next to the couches and chairs that she currently uses instead. She may also prefer a different material to scratch on, like cardboard or wood instead of carpet. Offer her a variety and see what she gravitates towards.
I would refrain from using squirt bottles on her as they might only be adding to her anxiety.
Instead of a calming collar, see if you can find some Feliway diffusers and spray. The spray is useful for discouraging scratching on stuff you don't want her to mangle (you spray it on the item, not her!) and the diffuser can help her to feel calmer. Google Jackson Galaxy and see if you can find some of his video blogs on cat behaviour. He's a total cat whisperer about situations exactly like this.
Good luck!
ETA - here's an article by Jackson Galaxy on using play therapy to treat random acts of aggression:
http://www.littlebigcat.com/behavior/play-aggression/