。
She was too short to see over the fence.
Literal
She [topic-は] height [subject-が] [too-low-低すぎて], fence's other-side [subject-が] could-not-see.
Two clauses linked by te-form (~て at the end of すぎ): 'being too short, (she) couldn't see ~.' ~すぎる ('too much') attached to an adjective stem (低すぎる) gives 'excessively low/short.' 塀の向こうがみえる is the standard 'see the other side of the fence' — note みえる takes が, not を, since 見える is a stative 'be visible to,' not an active 'see.'