The name Melvina is a girl's name of Celtic origin meaning "chieftain". Melvina and discussed in our forums with posts like "Girls Makeover - Two Middles".
From the experts:
Melvin doesn't deserve a feminine form, although plenty of parents -- many of them undoubtedly named Melvin -- disagreed in the 65+ years this name ranked on the Top 1000. To prove our point: There were ZERO baby girls named Melvina in the US in 2015.