Well I'm still learning all of this too, but I'll do the best I can to help!
Some things that stood out.
Hives reactions to milk is a serious one - definitely want to watch for even trace amounts in foods and x-contamination issues. Are you still breastfeeding? You would definitely
need to be avoiding all sources of dairy as well. Dairy can take a couple of weeks to be fully gone.
SISU is dairy free huh - the only dairy free one I could find when I was looking at the time was the Kirkman brand (some say they are diary free, but when reading the ingredients they list lactose, caesin etc.... very frustrating)
Hives reaction to the oats is also serious and sounds like gluten could be the issue? (oats are often x-contaminated with gluten) Has she reacted to other gluten sources? What other ingredients were in the baby cereal?
Yeast issues don't jump out at me in your case, so let's not worry about that for the moment.
If your not noticing a pattern with foods, have you looked into environmental triggers? molds, carpets, detergents?
For my DS's eczema I use a homeopathic cream by UNDA (Onguent 270 Zalf 270) I bath him everyday, put the cream on immediately after and it works wonders for us. Some other mama's use other creams, but I'm not sure what they are.
If you are just new to this, you may want to hold off just a little on reading the detox stuff just yet, b/c it's a lot of information to take in if you're just starting. (unless of course it doesn't confuse you as much as is does me
Personally I would start with
-eliminate all dairy sources (yours and hers)
- note any environmental factors, try a different bath/cream routine
- read the stickies on gut healing (bone broths, nutrients, whole foods to help heal her body)
There are some really smart mama's on here, sharing their knowledge. Read at your own pace, and ask questions as you go - good luck!