We don’t know exactly what happens there and Gregorovich probably wasnt the rightful owner anyway

She didnt actually beat him in battle, in fact she used accio not expelliarmus. Gellert had already lost what I assume is Grave’s wand when she “steals” it so no, she wouldnt be the rightful owner of the wand. I think Grindelwald probably already owns the wand, he’s just not using it at the moment