I'm going to focus solely on the question of the tricep bulging out and not address other comments on the pose.
1. It's a common problem, especially with a lot of women (who have less upper body strength). It's not about being overweight, just having some skin there that isn't muscle.
2. Have her turn her left hand so the fingers face the camera. This will usually reduce the bulge and also make it less obvious.
3. Put less weight on that left arm. Tricky to do without creating a stiff pose. But that bulge comes when you put weight on the arm. Use the arm as a prop, not for support. So she needs to lean back, extend that arm but not lean on it. For her build, that will make that upper arm quite slim.
4. Last resort--use liquify and reduce that bulging tricep.
I'm going to make one last comment about the pose in general but it helps the left arm. Have her twist at the waist more to the camera (so waist and below is side profile, above the waist is 1/4 to the camera). Twisting at the waist will take 5 pounds off. PLUS...it will also put more of the tricep BEHIND her and not in the view of the camera.