Yesterday, my student was asking about the G7 chord too. I showed her that the 7 is the F and I showed her in the root position: G B D F. I've also taught her some triad inversions so I showed her a neat way to play G7 with the RH:
1. Put RH in triad position like she normally does: G B D
2. Move the thumb one step down: F B D
In this way, her thinking is still in the root position with thumb moving down.
This is very helpful for her to think of the 7th Chords as a beginner.