I haven´ t seen Sara since she was a little girl, and she has changed beyond .

根据题目中的句子"I haven´ t seen Sara since she was a little girl, and she has changed beyond"可知，自从Sara还是个小女孩的时候，我就没有再见过她，她已经变得认不出来了。因此，空格处应填“recognition”，表示认出的意思。其他选项如hearing、strength和measure与句子意思不符。因此，答案为C。