How do you pronounce this Vietnamese name?

My friend's name is Minh Thu. Her American friends call her "Min Too" with a short i sound. Is the "h" silent in Vietnamese? When I hear her parents say it (immigrants from the North), it sounds like the "h" is a "g" like MING TOO. I hear it the same way when they say Ho Chi Minh (Ho Chi MING, not Ho Chi Min like how my American history teacher said it). The "i" is short in English when he said it, but her native parents use the long "i" in Vietnamese. Can someone explain this? Which one is the correct pronunciation?