The stuff needs to come off so she will be able to properly defecate. I would soak her for about 10 more minutes in warm epsom salt bath while gently trying to pick the stuff off.
After drying her well, apply some oil to soften it, in case it did not come off entirely.
This problem often happens with rumpless chicks too.
Do you have lactulose stool softener? It helps really good to flush everything out.
ETA: She will need something to perch on for the night, as sitting on the ground all the time while defecating will have her poop stuck to her butt.