Allergies can absolutely have an effect on this kind of reaction, but it's more likely to be food allergy related than from external products.
I would try to make sure that any soaps (laundry or otherwise) are "green," non toxic, and fragrance free, if possible. If you have a Whole Foods store or a good health food store in your area, you should be able to find products there that fit the bill.
Does your daughter eat a lot of wheat and dairy? If so, she could very well have yeast issues. How does her tongue look? Is there a white coating? That can be a sign of systemic yeast infection (although many people with chronic candida do not have the white coating, so it's not the only thing to look for).
About a year ago, I was diagnosed with candida and several other things. My doctor (an Integrative Medical specialist) took me off all wheat, dairy and sugar. Those three foods encourage yeast in the system, so the sugary drinks could have something to do with it if yeast is the issue. She also put me on a course of supplements. The one supplement she put me on to control the yeast is a probiotic supplement. Yogurt with active cultures is also a wonderful source of probiotics, so you might want to encourage your daughter to eat yogurt at least once a day. Yeast will not balance out by itself. It can take several months to bring the bacteria in the body back into balance, but starving it of wheat, dairy, and sugar is the best way to do it.
If you're interested in the diet that my doctor recommends, and how to follow it, I'll be glad to send an outline of it to you. It's really very easy to eat this way, and it makes a big difference. She recommends this diet to all of her patients, and in over 30 years of practice, she has never had a patient tell her that it didn't improve their lives.
I hope you find a solution to your daughter's condition. The poor thing must be miserable! I know I always have been when I've had a similar problem.