如图，菱形\(ABCD\)的对角线\(AC\)与\(BD\)交于点\(O\)，\(AB\)\(=5\)，\(AC\)\(=6\)，点\(E\)，\(F\)分别在\(AD\)，\(CD\)上，\(AE\)\(=\)\(CF\)\(= \dfrac{5}{4} \)，\(EF\)交\(BD\)于点\(H\)\(.\)将\(\triangle \)\(DEF\)沿\(EF\)折到\(\triangle {D}^{{{'}}}EF \)的位置，\(O{D}^{{{'}}}= \sqrt{10} \) ．
\((I)\)证明：\({D}^{{{'}}}H⊥ \)平面\(ABCD\)；
\((II)\)求二面角\(B-{D}^{{{'}}}A-C \)的正弦值．