C.N.
If she's developmentally delayed, then you may just have to let her wipe herself, and then check to make sure that she's clean until she is able to do it herself. And even adults sometimes miss a spot.
As for the stains, I learned while working in animal hospitals that hydrogen persoxide is perfect for removing blood and fecal stains from fabric without damaging the fibers or the dyes. We keep some in a spray bottle (make sure it's opaque, as light affects peroxide - that's why it comes in a brown bottle). Spray it on the stain, and let it bubble. Once it stops bubbling spray it again and toss it in the wash.