I get my RBO from my local Asian grocery store.
I poked around Japanese Google and it seems like rice bran soap is a fairly common beginner soap. From the videos and shop listings I saw, the oils involved very from fairly typical oil combos that experienced soapmakers use to 100% RBO soaps by beginners. I saw several mentions of people using ROE. My understanding is that the most important part of the soap is the
rice bran itself, which is a beauty ingredient dating back to the Heian era of Japan and is therefore quite beloved.
One idea is to make a small batch using a recipe that's familiar with you (based on your comments it sounds like you have experience) that you already know is good for sensitive skin, but subbing RBO for all or some of the Olive, adding in rice bran at trace, and maybe using rice water. See how your niece likes it.
You should take a look at
this thread for Ricey ideas. (I personally like to make rice soap with RBO, rice puree, sweet rice flour, and fermented rice water! People love it
)