Complex sentence: Sometimes she had to work on two or three posters per week, in addition to other work designing chocolate boxes, letterheads, packaging and magazine designs, and on one occasion, a luxury wall calendar.
Split into simpler sentences: Sometimes she had to work on two or three posters per week. She did not, however, only confine herself to posters; her other work included chocolate boxes, letterheads, and packaging and magazine designs; even, on one occasion, a luxury wall calendar.