When a man is divorcing his wife, does the fact that she is a convert (at the age of 3) make any difference to anything, especially in view of him witholding the get?
There is no difference between a girl born Jewish, and a convert, with regard to the divorce procedure.
There is a mitzvah to love the convert–even it is one’s wife or one’s ex-wife. Of course, this does not mean one should not get divorced. However, a husband must not manipulate the get as means of extortion or to cause suffering, the more so for a convert.