emulsion is best sponged off with water and a drop of WUL before it sets. Once hard, meths will break it down again, but you have to clean it off before it dries off and goes hard again. You can mix the meths with WUL to keep it from drying out, but this can mark absorbent materials.
Give it a wipe with white spirit and stick it through the washing machine?
It's not gloss paint but is white so can see it and although is DDs fault for not being more careful (we have the decorators in) I can't be doing with her getting flustered about getting a smart mark tomorrow if I can't get it off!