You sound exactly like me 4 years ago! My daughter is still teeny for her age, but has grown into the 10th percentile at age 6, so we're doing ok. People can be so insensitive, can't they? When folks make rude comments, I say "Isn't it amazing how different kids can be from one another?" Both of my kids are on the small side, and I love having little peanuts.
I know how stressed out you are feeling right now, and I hate wasting food too. Take a deep breath and remember that your daughter will not starve! She WILL eat when she's hungry, and it's perfectly normal for kids to go through these food jags. If you continue to offer her healthy, varied choices, lots of fruits and veggies, she'll learn healthy habits.
My advice to you is to continue to offer your daughter new foods at mealtimes. Experts say you have to offer something more than 20 times before a child will try it and like it. Keep it up! If you limit her to the foods she already likes, she will not learn to like other foods, and she won't get the balanced diet she needs. In our house the rule is you have to take one bite of everything on your plate (and if I'm making something new and different, I make sure one thing on the plate is something she'll love - just so I can be sure she's eaten something).
At dinnertime especially, try offering one food on her plate at a time. When my daughter was younger, she felt overwhelmed by a whole plateful of food (and I hated throwing it out afterward!) We gave her one "course" ate a time and she did much better. Another option is to serve her with a tablespoon. Start with literally one tablespoon of each food. She'll feel in better control of her choices, and you won't waste as much. She may even surprise you by asking for second helpings!
I'm not sure why, but multi-vitamins seemed to help my daughter's appetite. When I remembered to give them to her consistently, she seemed to eat more. Also, we had her on Pediasure shakes to give her extra calories. We kept her on whole milk, too. We also butter everything for her - I use Smart Balance because it's low-fat, high in Omega-3s and has no trans fat. She once asked "can I have butter on my bacon?" We drew the line there! :)
My daughter was the same way with snacks, so I would limit them, and make sure they were full of protein and low-sugar. Cheese sticks and Yobaby (made with whole fat milk) were staples in our house. I'd serve snacks at the kitchen table or counter, so she's not walking around with a bag of goldfish for hours on end. That may help with her appetite at mealtimes.
Hope this helps! Feel free to contact me if you have any more questions!