Lovely bold strokes and great simplicity of composition. The eye is immediately focused on the figure and then the arm leads the viewer's gaze away to other areas in the painting.
Perhaps what bothers you is the way the arm is stretched out? The lighter, oblique stroke just above her arm pit seems to suggest a stress point, like she's swinging her arm too far out for comfort? I'm not too sure, may be you'll need to check with the reference.
Slightly filling up the blue at the upper edge of the torso (to the immediate left of the armpit) with the adjacent flesh tint might release some of this apparent stress, along with raising the said oblique stroke to a higher level so as to better reflect the outline of the spine of scapula
. That's what it really is, I think. This lighter pink stroke at the present location would suggest the Teres Major muscle
, which in any case attaches on the inner side of the humerus, rather than on the outside. Could this have been the Teres Minor
- it could, but then that muscle is just too small, and the Deltoid
would've covered it anyway.
Just babbling to myself at this point, lol! Thank you for posting this delightful pic