my cat's health has rapidly declined since dental procedure

my 14 yr old cat stopped eating her dry food but still had a very vivacious appetite for canned food i was feeding her up to six or seven times a day since she wasn't "snacking" on dry. i took her to the vet to address a possible dental issue causing her to stop eating dry food. the vet recommended dental cleaning due to tarter and gingivitis and because my cat is "crazy" (my words) he wouldn't be able to tell more until she was under sedation. she went for procedure and they informed me she needed one "major" extraction and it was done. upon returning home she seemed fine ate fine and even tied dry food after a few days. within a week she started eating a little less and seemed to steadily decline slowly but at a point she just continued to slowly stop eating and when her breathing became labored about 2 1/2 weeks after dental procedure i took her back to vet. because of breathing difficulty they suggested chest x-ray and found fluid in her chest cavity around lungs and heart, her heart was not visible due to fluid and due to my own disabilities i have very limited funds i had already spent $300 for dental and $100 for x-ray so the vet sampled the fluid because clear fluid usually indicates a heart problem and it was clear, i couldn't afford to have it all pumped out but the started her on lasiks in hopes of removing fluid. she's been on lasiks for about a week and i do see improvement she isn't laboring to breath and is moderately active but isn't eating or at least very little to the point i'm afraid it isn't enough to sustain life and she asks me for something and when i offer it she walks away in dismay. i've tried everything i have 10 open cans of food in my fridge + baby food +chicken broth, tuna i've warmed it served it room temp,cold nothing is working. started her on a 1/4 pill of mirtazapine yesterday but no real improvement yet i'm a me i can't sleep,eat, all i do is cry. if she wont survive i don't want her to suffer, she doesn't seem well or happy i've had her since she was a week old i don't know what to do without her i feel the dental is to blame what could i have done?

I'm so sorry for you and your kitty.  I don't have any words of wisdom for you, just wanted to offer my sympathy.  Hopefully someone else will see this who can offer some advice.

So youre giving her the mirtzapine as an appetite stimulant?  Did the Vet say how long it might take for it to take effect?  Have you tried assist feeding her?  (with a needleless syringe, making her food soupy, then filling up the syringe and putting it into her cheek and slowly giving it to her?)

As I'm sure you know, she must eat.  Cats cannot go too long with eating or their livers shut down and create worse problems.  Is she drinking? 

for your girl