Slatternly, dowdy, frowzy, blowsy can all mean deficient in neatness, freshness, or smartness, especially in dress or appearance.
Slatternly stresses notions of slovenliness, unkemptness, and sordidness.
Dowdy is likely to imply a complete lack of taste typically marked by a blend of something untidy, drab, or tawdry.
Frowzy suggests a lazy lack of neatness, order, and cleanliness, but frowzy also may apply to a natural and not unwholesome disorder or it may suggest drab misery and squalor as an inevitable result of circumstances.
Blowsy implies dishevelment or disorder to which is often added a notion of crudity or coarseness or grossness.