Dear Emma,
It's great to hear you're interested in working at the Body Shop! Your summer job experience sounds valuable. You mentioned liking the training and the useful nature of the job, which are excellent points.
Your skills in teamwork (running the school shop) and your proactive approach to seeking experience are impressive. Your interests in yoga and music show a well-rounded personality.
Regarding your CV, the information about your upcoming GCSEs and your previous work experience at the Body Shop is well-supported by your letter. Keep highlighting these aspects!
Best regards,
[Your Name]