Hi,
Just to add something I didn't see in your responses: I've had food allergies all my life, which places me squarely among the last generation of kids who grew up feeling crummy and not knowing why (food allergies weren't recognized yet). I doubt your granddaughter has an "allergy" to starchy foods per se, but it might be safe to say they make her feel lousy. I clearly remember being stuck in my highchair and avoiding foods that made me 'hurt' or 'sick.' e.g.: Spaghetti gave me headaches and I felt sick clear down to my bones -- Twenty years later, I found out I was allergic to rosemary, the key ingredient in Mom's sauce. Same story with several other foods. Mom felt terrible when we both realized why I'd been a picky eater all those years. (It wasn't her fault, though!)
Your granddaughter is avoiding starchy foods? I'd check out glucose-free options. Look at the ingredients in your pasta and see if there are any common links to other things she avoids. Processed foods are a nightmare -- they have so many things hidden under so many different names that it's tough for a normal person to tell what's what. Stick to really simple foods and start a list of what she avoids. Then adjust her menus.
You're pretty safe if she's a veggie eater - there are SO many options to fill out a healthy diet for vegetarians. Soy's a great resource. It's when they'll only eat fat and carbs that you need to worry.
And, btw, my youngest is the same way: rail thin and frighteningly light appetite. Around age 4, we noticed a pattern -- for about three weeks every 'once in a blue moon' she'd eat like a teenage quarterback. That kid could clean out the fridge and ask for seconds! Then POOF! the appetite would disappear as fast as it came. About two weeks later, sure enough, all her pants were hi-waters. She'd grown about three inches... and still thin as a rail. But she's the fastest runner in her class and she's healthy as can be. (For what it's worth.)
Good luck!
:-)
PS: You ROCK for being such an involved and caring part of your family and church! That's what family is supposed to be like -- bravo!