。
She's used to speaking in public.
Literal
She [topic-は] in-public [at-で] speaking [nominalizer-こと] [to-に] is-accustomed.
Uses the pattern ~ことに慣れている ('to be accustomed to doing'). The nominalizer こと converts the verb phrase 人前で話す into a noun clause, and に marks it as the target of 慣れる ('to get used to'). The resulting state expressed by ~ている tells us the acclimatization is complete — she's already comfortable, not in the process of adjusting.