I am sorry your cat is having to go through this. Certainly syringe feeding baby food is an option. If you are unable to get medication into her it is unlikely you will be able to get an appreciable amount of food into her. If she has a confirmed, terminal cancer her decision to stop eating may be her indication that she no longer wants to carry on. If her cancer is a type with a high cure rate, force feeding her through the treatment is a viable choice. Has she been classified as terminal? If not, consider force feeding through her treatments.