The arm position in that video is essentially from the anus going superiorly to the receiver's upper left quadrant, them bending her elbow to extend farther into the colon going to the receiver's upper right under the ribcage.
The maneuver has to be done with the giver's right arm for her to be on her knees leaning forward. Had she used her left arm, she would have to be almost on her back to make her left arm bend ion the direction of his colon.
I have never gone as far as she did. I have to show this clip to my husband. Being the competitive type, I know he will at least let me try. I don't have Olympic weight lifter's arms, but mine are bigger than hers, so I don't think I'll be able to do it with him. I'll let you know if I get anywhere near her amazing depth.