、。
She might have been startled when she got my letter.
Literal
She [topic-は] my letter [object-を] receive-and, was-startled [might-かもしれない].
受け取る is the verb for physically receiving something handed or delivered — distinct from もらう (be given) or 受ける (accept, undergo). The mimetic-derived びっくりする captures a sudden, gut-level startle rather than a measured 'surprised' — closer to 'jolted' in feel. かもしれない hedges the whole proposition: the speaker is guessing, not asserting. The 連用形 (te-form) 受け取って chains the events sequentially: she received it, then this reaction may have followed.