。
She gets seasick easily.
Literal
She [topic-は] easily seasickness does.
船酔い ('seasickness') is a transparent compound: 船 ('boat / ship') + 酔い ('intoxication / sickness from motion or alcohol'). The same 酔い appears in 車酔い ('carsickness'), 飛行機酔い ('airsickness'), and 二日酔い ('hangover' — literally 'two-day intoxication'). Adding する turns the noun into a verb: 'to get seasick'. Plain non-past 船酔いする expresses the habitual tendency, not a specific event — 'gets seasick' as a general fact about her constitution. すぐ here means 'easily / readily' rather than 'immediately'.