I wouldn't suggest switching formula as that can actually lead to more issues. Especially since soy is a high allergen!
Juices could actually make the problems worse because of the sugar in it. Stick to binding foods that she's already had (bananas, rice, apples, toast). Yogurt has probiotics that are good for digestive health, so if she's already had yogurt and that doesn't cause her to have diarrhea, yogurt would be beneficial. Pedialyte either in a cup/bottle or they have freezer pops are good for hydration.
Don't try anything new because you won't know if it the food that is causing the diarrhea.
Also, its possible that teething could be the source. It might last a week or two if its a bug, and she may lose a little weight, but she will be fine. As L. as she has at least 4 wet diapers throughout a 24 hour course, she's hydrated enough (they may not be as wet as normal, but she won't wet them at all if she's dehydrated).
We've been through a couple stomach bugs with my son, who turned 1 today, just stay calm, give her extra love and wash your hands so you stay healthy.