Well if she really wants to improve her massage game I can give a few pointers. I am a highly untrained, forever alone purveyor of adult manga after all which clearly means I am a (non)professional.
She could try doing it from behind for better angle of grip and to double as a hug to really catch those feelings.
If she's adamant about doing it from the front then might I suggest insuring a comfortable, firm yet gentle grip making sure to cup the breast from below and the front.
Now as for the actual massaging part now that the handling is out of the way. (unlike her boobs.)
Squeeze gently and use a slow up and down motion while slowly going in circles.
For a bit more pleasure you can use your index finger to further message the nipple itself or even the index finger and thumb for some pinching and rubbing or kneading. Gently of course.
If any masseurs or females could corroborate and or add to this that would be helpful.