How did Moegi acquire the Wood release Wood release is the kekkai genkai of the Senju clan (originally the God trees sacred ability and also the Otsutsuki clans Kekkai Genkai), however, Moegi is able to do it by combining Water and earth style. Does this mean being able to combine 2 elements can allow anyone to use an advanced element?  We know Orochimaru used to perform experiments on merging Hashirama's cells with small children but Sarutobi Hiruzren (the Third Hokage) put an end to it.

Moegi did not have the wood style ability while she was younger plus the experiments that Orochimaru did with Hashirama's DNA were destroyed earlier in the series. So how did Moegi suddenly become able to use it at adulthood?
One thing before i answer the question: wood style is not the senju clans bloodline. in order for it to be a clans bloodline, multiple people in said clan would have to be able to use it. i believe that hashirama was able to use wood style due to being the reincarntion of asura. asura is an otsutsuki and as we found out, the otsutsuki clan can use wood style. as for how moegi can use it i believe that she is capable of using yin-yang release and combine it together with her water style and earth style thus creating wood stlye. now before you say i'm wrong think about this: hagoromo was able to CREATE life by utilizing yin-yang release. also, yin release creates form from nothing while yang release creates life, combine those two and you have a living life form. this is just my theory. hope this helped :) 
Edit: genjutsu uses yin release, Outer Path's ability uses yang release, Creation of All Things utilizes yin-yang release, using both imagination to make the Tailed-Beasts bodies while at the same time gives life to forms without any. 670 page 17, 449 page 1-3