Help save my cat

My cat Angel got sick about a month ago and it hasn't gotten better. She hasnt eaten in 3 weeks and I've had to wet her chin to get her to drink any water. My mom called some vets and they all said she was dying, before I have to put her down I want to see if there is anything I can do to save her. Shes been my best friend for 13 years now and she was completely fine with no signs of sickness until last month.