The phrase "hard G" refers to the pronunciation of the letter "g" as in the word "gate," where the sound is produced at the back of the mouth. The letter "g" can also be pronounced as a "soft G," as in the word "gem," where the sound is produced at the front of the mouth.
The word "girl" is pronounced with a soft G, as in "gem." The "g" sound is produced at the front of the mouth, not the back.
Therefore, the statement "a girl has a hard G" is incorrect. The word "girl" has a soft G.