What is grammatically wrong with saying, "She showed me it." I know that should be showed it to me but I can't think of the reason the first is wrong. Thank you.
Linguists will sometimes talk about the "weight" of a phrase. This refers roughly to the length. For example, you can say "She showed the dirty spot on the floor of the house to me" or you can say "She showed me the dirty spot on the wall of the house" because "the dirty spot on the floor of the house" is long enough that it doesn't disrupt the cadence/stress pattern of the sentence. "She showed me it" has four stressed syllables in a row, accounting for 100% of the syllables in the sentence.
It's not so much ungrammatical as it is awkward, so it's avoided.