I just did a soy challenge on my boy.
What I did was have some soy ice cream & then waited to see how long it would appear in him, if at all.
We had an epic fail!
I ate a normal serve at about 9 at night, within 15 mins I was wheezing & had to take my inhalor
then I woke the next morning with a massive headache & felt like crap & didn't want to go far from the house.
The first he feed off me was 6am the next morning. He'd slept through. About 6pm he did the most aweful poo which I delegated to DH & then discovered it had gone down his legs. He also didn't sleep the whole night. Skin was red through the nappy area as well, where as earlier during the day it was nice & pink. Not sure what is going to happen today.
What I had planned on doing was having some ice cream each night & see what happened. We both reacted so quickly that I've knocked that on the head. The other thing I was going to do was drink a glass of soy milk at lunch time. I might give that a go next week & see how he goes with that, although I'm really unsure about it.
So I would start just by drinking a standard glass of milk each day & see how she goes. Based on what happened to me you should see a reaction in 24 hours. Drink one glass at the same time each day & see what her tolerance level is. It could take a few days? If I had dairy usually the next day or two I'd see some chunky spilling. But I usually only have a one off sneaky of something dairy.