Dhanesh said, "This girl is the wife of the grandson of my mother." Who is Dhanesh to the girl?

Let's decode the statement made by Dhanesh step by step:
1. "My mother's grandson" $\to$ Dhanesh's son (or nephew, but primarily son in direct linear relation context).
2. "Wife of the grandson of my mother" $\to$ Wife of Dhanesh's son $\to$ Dhanesh's daughter-in-law.
3. Since the girl is Dhanesh's daughter-in-law, Dhanesh is her Father-in-law.