'Margie' is a diminutive form of Margaret /m'a: grit/. It is normally pronounced as [mˈɑːdʒi] by the native speakers. Some other derivatives include Maggie, Meg, Megan, etc. Now, all of these have the hard /g/ sound. So, I feel Margie may be pronounced as /m'a: gi/. So far, I've found just one reference that supports it.
So, how should a teacher of ESL teach the learners its pronunciation in a country where the name is quite unfamiliar? Will it be wrong to read it with the hard /g/?