Congrats Neem for the good deeds. I'm so sorry to hear what had happened later on. In my opinion, matters turned serious bcos u told the girl that she must pay for the expenses. We didn't know whether or not the girl hv money problem or she just refused to pay. I doubt, the girl lied when she said that she's going to KL and asked you to keep her cat until she return for it. She's actually needed some time - either to find money, or to think of her next action. Obviously, her nx action was to send u the rude sms and get her father to get back the cat for her (thinking that u must be afraid of her father and will let go the cat without saying anything....where in reality, despite anger, u shouted back to her father).
Moral of the story :
1. When u rescued an animal, take a picture as a proof on how bad his / her condition the mmt u found him / her.
2. This is troublesome, but we learned thru experience....lodge a police report. Also tell the police what actions that you had taken so far such as putting up posters, advertising in the net, the treatments and so on. U can show the police report and a copy of the poster to the owner. This will make the owner think 100X before accusing you of stealing the cat.
3. Since you didn't know the owner as yet, and the cat really needs vet attention ASAP, set yr mind that you will not claim any $$$ you spent for the cat for treatment, medications etc. Else, send the cat to a government vet (which is normally way cheaper).
4. Get a vet's report on the condition of the cat, the treatment given & keep all receipts for the payment. Show all these to the owner and let the owner consider about the repayment.
Just my two cents