Hello, and welcome!
I'm so sorry Cassie isn't feeling well.
There are many possibilities for the symptoms you describe, for example, she may have an upper respiratory infection (URI), analogous to our human cold; since you heard a rattle when she breathes, now, she could have bronchitis or asthma. Here is more information:
As you can see at the site above, heartworm disease may be possible, Feline Leukemia or other immunodeficient diseases must be tested for.
A heart problem like congestive heart failure is also a possibility, with fluid around the heart or around the lungs.
She also may have the herpes virus (not contagious to humans), which causes respiratory symptoms and also can affect the eyes. For this, L-lysine, a amino acid supplement, is effective. Here is more information:
You can find this in natural food stores and also, as you can see, there are special formulations just for cats. However, I would not advise giving Cassie any OTC supplements until consulting with her vet.
Unfortunately, there's not much you can do at home for Cassie, and she needs to be seen in person by a vet, asap in order to be diagnosed and treated. This animal hospital below, is nationwide and offers a free coupon for new patients/first visits; hopefully, you have one near you, so this will save you some money:
It's also possible that she may have aspirated some of the water you were dropper feeding, into her lungs, if it 'went down the wrong way.' Dropper feed her from the side, not the front of her mouth, where you will find an opening between her upper and lower teeth. Squeeze in a little bit at a time and then wait for a swallow. You can rub her throat to help encourage the swallow reflex.
It's also dangerous to her health to not eat for even a short time, as this can cause serious liver problems, like hepatic lipidosis or 'fatty liver.'
Because she is so small and may have a viral or bacterial infection in her system or her respiratory system, or another underlying medical problem, it would be advisable to have her evaluated in person by a vet, as soon as possible to get a definite diagnosis and treatment. Since this started yesterday, you can bring her to an ER vet center near you, if your vet is already closed or has no emergency hours.
I hope all will be well with your sweet Cassie and please let me know how she's doing and what the vet tells you. Thanks!
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