Dirty Sim

Try having her travel to another lot and back and see if that helps.
If the issue remains, repairing the game may help.
Also, if you  use mods/cc,try moving the whole mods folder to another place, delete the localthumbcache.package and then test to see if the issue remains without mods/cc there.

Did you get the new pack? That’s not one of the ailments, is it? (I remember promos about an “urge to create” or something like that and the sim would have paint on them).

PipMenace​  is right! It is the effect of the “Creation Impulse” ailment. If you create a cure for this on the apothecary table, the paint will be removed.