A.not her being ableB.her being not able

C.not being ableD.that she's not able to

【答案】C

【解析】

考查动名词作宾语。句意：她为不能来而道歉。空格处作介词for的宾语，用动名词；be able to do为固定搭配，意为“能够”。故选C项。