A.,
You are right, most doctors do not respect parental knowledge/intuition, but don't let that dissuade you. Doctors don't know everything, so just because they don't think it's a "big deal" doesn't mean there is nothing going on. It just means that you are going to have to do some legwork and deal with the problem on your own. You could also talk to a dermatoligist or an allergist. The naturopathic doctors have some wonderful insights on food reactions that you may not get at a traditional allergist.
Your girl may not actually have an "allergy," but food intolerances and reactions are very common. Technically, an allergy means that your immune system kicks in with a response. This might show up as hives, runny nose/watery eyes, or the most dangerous, an anaphylactic reaction. Even if a child is not technically allergic to a food (in that their immune system is not responding) they can still get a bad reaction to it. Some kids get gastrointestinal problems - gas, bloating, diarrhea - and sometimes its a dermatalogical problem - rash, redness, sensitivity. Sometimes it is a behavioral reaction - my friends sons go completely ballistic when they eat food with red dye in it. No matter what the root cause is, the treatments is the same - you need to avoid the food that is causing a reaction. Additionally, you can definitely develop both allergies and reaction to certain foods over time. Just because your daughter has been eating a certain food for a while does NOT mean that she is not reacting to it now.
It sounds like you have an idea what foods are causing these rashes. I would start by eliminating these foods entirely and seeing how it affects your daughter. If the rashes go away, then you know how to deal with the problem; just don't feed your daughter those foods. In a few months to a year, you can try them again and see if she still reacts. As children grow older and their body systems get more developed, they sometimes grow out of allergies/intolerances.
It can be difficult to try to track down these kinds of things in your kids. Your daughter is very lucky that you are concerned and diligent enough to pursue it. Keep trying, and you'll figure it out!
Best of luck,
S.