Tube feeding rays is very possible. I go to it as a last resort.
Blend a slurry of seafoods together. I'd mix in a little B12 (you can get tablets at any health food store). I'd also add a high calorie supplement (Nutra-Cal or STAT). Those two additons will help get her eating again, and get her through the time she's not.
Once it's blended, use a syringe and airline tubing to feed the animal. It won't take much food for her at this size. Make sure to round the tip to the airline so it's not a sharp edge. Tubing is a two person job. Catch the ray and invert her. The person holding the ray should have a finger or two on her back near the base of her tail to feel her stomach. The other person runs the tube into her mouth SLOWLY. If you push too hard, you can do damage to the lining of the stomach wall. Once it's in, pull it out just a touch. At that point, I'd mark the tube with a black line or other marker so you know the depth to insert next time. Slowly push the food in. If she fights or regurges, let her go. It's not worth stressing her out over it. Give her 7mL or so to start with. Small amounts a couple times a day will be better than large amounts once.
