。
She's leaving for New York this Sunday.
Literal
She [topic-は] this-coming Sunday [on-に] New-York [to-へ] departs.
Two location/time particles do separate work here: に marks the time point ('on Sunday'), へ marks the direction of motion ('toward New York'). Mixing に and へ in one sentence is normal because they don't compete for the same role. The verb 出発する is the formal Sino-Japanese 'depart'; less formal alternatives include 出る ('leave') or just 行く ('go'). Note the polite ~ます form contrasts with the more literary tone of 出発する — Japanese often combines neutral politeness with elevated vocabulary.