I hope you don't mind, I talked to a Cloth Diapering expert friend and asked her advice on getting rid of the yeast rash.
You have probably tried most, if not all of this, but here is what my CD friend said! First, she mentioned that Probiotics, since they stay in your gut, probably aren't passing through to your DD2. She said that you can get probiotics in liquid form, but you probably should give her something. (I have no idea... so maybe ask around?)
Second, she said the yeast rash will live in any fabric that touches the kids skin and not just the diapers! :-O I hadn't thought of it possibly being in things like towels or sheets and transferring back to them. She recommended adjusting your hot water heater to over 122 degrees to make sure that when you wash it's REALLY hot. She recommended using an Oxy-Bleach (Oxyclean, or something similar) in every single load you wash until at least a week after the rash has disappeared. She also recommended Motherlove's Diaper Rash & Thrush cream to treat the rash:
https://www.motherlove.com/product/2301_DR-Diaper-Rash-and-Thrush.html. The ingredients list is at the bottom of the product description so you can make sure its allergy safe for your family

Lastly, do your DDs share diapers? I know that you've said they are very similar in size. It is possible that one is re-contaminating the other.
I hope that some, or any of this is helpful! I've also found this resource:
https://www.pinstripesandpolkadots.com/YeastvsCloth.htm. I love Pinstripes and Pokadots, I check with them on so many other things, I just did a websearch figuring they would have something about killing a yeast rash! My friend said the most annoying and frustrating thing about yeast rashes is to make sure that you kill it out of every fabric possible. It will be in towels, sheets, clothes, washcloths, even on fabrics that the rest of the family uses.
She recommended to make sure that you maintain the diligent wash cycle long enough after the rash is visibly gone, to kill it permanently (at
least a week). Its also possible you might need a stronger detergent for your CDs until the yeast is gone, I remember you saying that you make your own. Pinstripes and Pokadots also has a list of CD safe, mostly eco-friendly degergents:
https://www.pinstripesandpolkadots.com/detergentchoices.htm. I have recently switched to the Ecos brand and it seems to work for us fine. She strongly recommended things like Tea Tree Oil, Grapefruit Seed Extract, Myrr, and Oxy-bleach (non-chlorine, so it's color safe).
Hope something works! Good luck, my friend!
Re: @+adamwife+
Right ovary removed 09.04.2012 via vertical laparotomy
Essure implant placed on remaining tube 06.13.2013; successful followup scan 09.30.2013
They used to think that probiotics could not be passed through breastmilk, however, newer research is showing that it can. Regardless, breastmilk in itself contains probiotics. DD2 also eats yogurt daily, so we're good there!
I'll have to check out some of the things she has suggested. I read on another site about grapefruit seed extract and how it works better than TTO, so I think I'll give that a try first!
@Rynleigh DD2 has always been prone to diaper rashes and gets them even in disposable diapers, but whenever these particular cloth diapers are on her and get wet, the rash turns yeasty with the red pinpoints on it. She doesn't get that same type of rash in disposables. It could be that the fabric is irritating her skin and then allowing the yeast that I can't get out of the diapers to enter her bloodstream, like you said. She eats zero sugar, eats a diet high in probiotics, and has never had an antibiotic. I just think she is prone to diaper rashes and once the skin is irritated and she comes in contact with these diapers, the yeast thrives. It's so irritating.....for both of us.
DD1 also gets a yeasty rash whenever she wears the diapers, although she isn't as prone to diaper rashes in general in the disposables. If the yeast can't live in the diapers and be passed back and forth between the girls, then why are they both getting the rashes?
I've never dealt with this issue in six and a half years of cloth diapering. The only difference in the last few months is that I began a diet to starve off the candida overgrowth in my own body (GAPS). It makes me wonder if my diet changed my breastmilk somehow and caused this yeast overgrowth in DD2 (and then in turn DD1). That's all I can think of. I'm using the same detergent, wash cycle, and everything else that I always have...
That website is a great help! Thanks!
I have used Ecos brand when I run out of homemade detergent, so I'm glad that it is on the safe list. Maybe I'll just switch to it for diapers from now on, just to be safe!