A 'werkster' is only a maid (often cleaning in elderly people's houses). Often 'huishoudelijke hulp' (domestic help) is used.
Another word for someone who cleans stuff is 'schoonmaker' (for men and women) and 'schoonmaakster' (for women).
There are quite some words for 'worker': 'arbeider', 'arbeidskracht' or just 'kracht', or 'werknemer' (employee). Sometimes 'werker' or 'werkster' is used, but that's usually with an adjective, for example 'maatschappelijk werkster' is 'social worker' (female).