Just to start out, I won't advise against taking her off her meds. However, I would not rely on Pediasure or V8 as an adequate source of nutrition as it is packed with sugar, carbohydrates and with V8 sodium. I think your goal should be to make each meal that she does eat as nutritionally dense as possible to be sure she is getting all her requirements. I think that many people in this situation would automatically think sweets or treat foods to tempt the child to eat, but as you know the sweets provide calories, not nutrients and can actually cause her to gain fat, but lose muscle.
Consider making her healthy smoothies. She might view these more as drinks rather than food. At Whole Foods or maybe even Sprouts you can buy Amazing Grass Green Food drink powders. They don't taste great alone (mixed with milk or water), but blended in a smoothie, it packs it full of essential vitamins and nutrients. It comes in a chocolate version and berry version too. It's a bit expensive to buy, but you only use about a tablespoon or less at a time, so one jar will last you a while. Just be aware they don't have added sugar, so if you buy the chocolate, add a few drops of liquid stevia to sweeten it.
If she'll eat them, try to provide monounsaturated fats like avocados, olives, nuts, etc. Also, starchy carbs are probably ok too like potatoes (not processed like Or-Ida or french fries), sweet potatoes, carrots and corn. I think a book called Super Baby Food has some whole food health choices for weight gain that you might want to check out. Don't let her see you with it ; ) I seem to remember a friend's baby needed to gain weight and she had a lot of success using that book as her guide.
Also, check with your healthcare provider to see if you can visit a dietician in network. That person can also help you with some more options.
If you want it, I have a breakfast shake/smoothie recipe that's really nutritionally dense. Of course, you can make it any time of the day. My kids drink these and 2 of the 3 are very picky. You can also use it as a base to experiment with other ingredients. I won't force it on you. Just send me a private message if you do.
K.
SAHM to 3, ages 7, 5 & 3